Forces Flashcards
1
Q
What are the two types of quantities in physics?
A
A scalar and a vector
2
Q
What is a scalar?
A
A quantity that has only magnitude
3
Q
Give an example of a scalar quantity.
A
Mass
4
Q
What is a vector?
A
A quantity that has both magnitude and direction
5
Q
Give an example of a vector quantity.
A
Velocity
6
Q
What is the difference between distance and displacement?
A
Distance measures the path length, while displacement measures the shortest distance between two points with direction
7
Q
What is the significance of representing vectors with arrows?
A
The length represents magnitude and the direction indicates the vector’s direction
8
Q
What is a contact force?
A
A force that acts between objects that are physically touching
9
Q
List four examples of contact forces.
A
- Friction
- Air resistance
- Tension
- Reaction force
10
Q
What is a non-contact force?
A
A force that acts at a distance without contact between bodies
11
Q
List three examples of non-contact forces.
A
- Gravitational force
- Electrostatic force
- Magnetic force
12
Q
What is weight?
A
The force acting on an object due to gravitational attraction
13
Q
How is weight measured?
A
In Newtons (N)
14
Q
What is the relationship between mass and weight?
A
Weight depends on mass and the gravitational field strength
15
Q
What is the unit of mass?
A
Kilograms (kg)
16
Q
What is the centre of mass?
A
The point through which the weight of an object acts
17
Q
How can the centre of mass of a symmetrical object be found?
A
It is located at the point of symmetry
18
Q
True or False: Mass and weight are the same.
A
False
19
Q
Fill in the blank: A _______ is a force that opposes motion.
A
Friction
20
Q
What is thrust?
A
The force causing an object to move, such as from a rocket engine
21
Q
What does a free body diagram represent?
A
The forces acting on an object
22
Q
What is tension in the context of forces?
A
A force transmitted through a cable or string when pulled
23
Q
What is the role of a normal force?
A
It supports objects resting on a surface and acts perpendicular to the surface
24
Q
Define gravitational attraction.
A
The attractive force experienced by two objects with mass
25
What is the effect of gravitational force on objects?
It keeps objects firmly on the ground and causes them to fall
26
What is the common misconception about weight?
That weight and mass are the same thing
27
What device is used to measure weight directly?
Calibrated spring-balance or newton-meter
28
How can mass be converted from grams to kilograms?
By dividing the value by 1000
29
Describe what happens to the centre of mass of a human body when leaning forward.
It shifts lower than when standing upright
30
What is the definition of the centre of mass?
A hypothetical point where the mass of an object is concentrated
## Footnote
The centre of mass can lie inside or outside of a body and shifts depending on the shape of the body.
31
How does the centre of mass of a human body change when leaning forward?
It is lower compared to when the person is stood upright.
32
What is the difference between mass and weight?
* Mass is measured in kilograms (kg)
* Weight is measured in newtons (N)
* Weight is the force of gravity on a mass.
33
What is the relationship between weight and mass?
They are directly proportional.
34
What does the gravitational field strength (g) represent?
The acceleration due to gravity, which is 9.81 m/s² on Earth.
35
True or False: Weight and mass are the same.
False
36
What is the gravitational field strength on the Moon?
1.63 N/kg
37
How does weight change on different planets?
Weight will differ depending on the strength of the gravitational field.
38
Define resultant force.
A single force that describes all of the forces operating on a body.
39
What is the difference between balanced and unbalanced forces?
* Balanced forces cancel each other out, resulting in no resultant force
* Unbalanced forces do not cancel out, resulting in a net force.
40
Give an example of balanced forces.
The weight of a book on a desk is balanced by the normal force of the desk.
41
What happens in a tug-of-war when one person pulls with more force?
The forces are unbalanced, resulting in a resultant force in the direction of the stronger pull.
42
How do you calculate resultant force?
By adding or subtracting all of the forces acting on the object.
43
Fill in the blank: Friction always ______ the motion.
opposes
44
What is tension?
The force experienced by a cable, rope, or string when pulled.
45
What is normal contact force?
The force acting at a 90° angle to the plane of contact between two objects.
46
Define upthrust.
The upward buoyancy force acting on an object in a fluid.
47
What is the purpose of free body diagrams?
To model the forces acting on an object.
48
What must be true about the arrows in a free body diagram?
* They are scaled to the magnitude of the force
* They point in the direction of the force
* They are labeled with the name of the force.
49
What is the significance of resolving forces?
It allows for accurate calculations of resultant forces.
50
How can a single force be resolved?
Into horizontal and vertical components.
51
What is the triangle method in vector addition?
A method to combine vectors by linking them head to tail to form a triangle.
52
What is the parallelogram method?
A method to combine vectors by drawing a parallelogram and using the diagonal as the resultant vector.
53
What should you always include in force calculations?
Units and direction of the force.
54
True or False: The resultant force is sometimes called the net force.
True
55
What is the first step to find the resultant vector using scale diagrams?
Decide on a suitable scale
## Footnote
A scale of 1 cm to 1.0 kN is the most suitable for this scenario.
56
What is the second step in creating a scale diagram for resultant vectors?
Use grid paper to draw the vectors top to tail and to scale
57
What should you do in the third step after drawing the vectors?
Draw the resultant vector and measure its length
58
In the fourth step, how do you convert the length of the resultant vector to kN?
Use the scale to convert the length to kN
59
What does a resultant force length of 8.6 cm represent?
The resultant force is equal to 8.6 kN
60
True or False: Students often find scale diagrams easy to begin with.
False
61
What type of scale is recommended for beginners when drawing scale diagrams?
1 square or 1 cm is equal to 1 unit
62
What should students remember to bring to the exam when working with scale diagrams?
A ruler and a sharp pencil, and a rubber
63
What is the suggested strategy when first scanning the exam paper?
Look for scale diagram or graph plotting questions
64
Why is it important to allocate time for scale diagram questions?
They are more involved question types that require careful execution
65
What is work done?
Work is done when an object is moved over a distance by a force applied in the direction of its displacement.
66
When is work not done?
No work is done if a force is applied to an object but doesn’t result in any movement.
67
Give an example of work being done.
Work is done on a ball when it is lifted to a height above the ground.
68
What does the weight of a ball do when it is lifted?
The weight produced by the gravitational field does work on the ball over a distance equal to the height of the ball.
69
What is the formula for calculating work done?
W = F × s
70
What do the variables W, F, and s represent in the work formula?
W = work done in Joules (J), F = force in Newtons (N), s = distance in metres (m).
71
How do you calculate the work done by brakes on a car?
Use the formula Work = F × s with known values for force and distance.
72
Calculate the work done by brakes applying a force of 500 N over 23 m.
Work = 500 N × 23 m = 11,500 J.
73
What is the unit of work?
Work is measured in joules (J) or newton-metres (N m).
74
What is the relationship between joules and newton-metres?
1 J = 1 N m.
75
What happens to energy when work is done?
Whenever any work is done, energy is transferred from one store to another.
76
What is the energy transfer pathway for mechanical or electrical work?
Mechanical (or electrical) working is an energy transfer pathway.
77
How is energy transferred related to work done?
The amount of energy transferred (in joules) is equal to the work done (also in joules).
78
What happens to energy if a force acts in the direction of movement?
The object will gain energy (energy is transferred to its kinetic store).
79
What happens to energy if a force acts opposite to the direction of movement?
The object will lose energy (energy is transferred away to the thermal store).
80
Describe the energy transfer when raising a bucket out of a well.
Work is done as a force is exerted to pull the bucket up, transferring energy to its gravitational potential store.
81
Calculate the energy transferred to a bucket raised 15 m with a mass of 10 kg.
Energy transferred = 10 kg × 9.8 N/kg × 15 m = 1470 J.
82
What is friction?
Friction is a force that works in opposition to the motion of an object.
83
What effect does friction have on energy transfer?
Energy is transferred by heating, raising the temperature of the object and its surroundings.
84
What causes a rise in temperature due to work done against friction?
The work done against the frictional forces causes this rise in temperature.
85
What is air resistance?
Air resistance is a type of friction that slows the motion of an object.
86
What happens to an object when it moves through the air?
Particles bump into the object, causing energy transfer by heating due to work done against frictional forces.
87
True or False: Work done against friction causes a temperature rise.
True.
88
What does the weight equation relate to in terms of work done?
Weight = m × g, which can be substituted into the work equation.
89
Fill in the blank: One Joule is equal to the work done by a force of one newton acting through _______.
one metre.
90
What must be applied to change the shape of stationary objects?
More than one force
## Footnote
Forces can cause stretching, bending, or compressing.
91
What are the three ways an object's shape can change?
* Stretching
* Bending
* Compressing
92
What is an example of compression?
Placing a mass on top of a spring on a flat surface
## Footnote
The weight of the mass and the reaction force from the surface act towards each other.
93
What is an example of stretching?
Placing a mass on the bottom of a vertically hanging spring
## Footnote
The weight of the mass and the tension in the spring act away from each other.
94
What causes bending in an object?
Forces acting at different points on the object
## Footnote
Example: A diving board bending when a swimmer stands at one end.
95
What is the difference between elastic and inelastic deformation?
* Elastic: returns to original shape
* Inelastic: remains distorted
96
Give examples of materials that undergo elastic deformation.
* Rubber bands
* Fabrics
* Steel springs
97
Give examples of materials that undergo inelastic deformation.
* Plastic
* Clay
* Glass
98
What does Hooke's Law state?
The extension of an elastic object is directly proportional to the force applied, up to the limit of proportionality.
99
What is the equation for Hooke's Law?
F = k × e
100
What does 'k' represent in Hooke's Law?
Spring constant in newtons per metre (N/m)
101
What does 'e' represent in Hooke's Law?
Extension in metres (m)
102
How can the extension of an object be calculated?
Final length - original length
103
What is the limit of proportionality?
The point beyond which the relationship between force and extension is no longer directly proportional.
104
True or False: Hooke's Law applies to all materials.
False
## Footnote
Some materials do not obey Hooke's Law and have a non-linear relationship.
105
What does a straight line on a force-extension graph indicate?
The material obeys Hooke's Law.
106
What is the significance of the gradient of a force-extension graph?
It represents the spring constant.
107
What is the equation for calculating work done on a spring?
Ee = ½ × k × e²
108
What does Ee represent in the work done equation?
Elastic potential energy in joules (J)
109
How does the extension affect the work done on a spring?
If the extension is doubled, the work done is quadrupled.
110
What is the aim of the required practical investigating force and extension?
To investigate the relationship between force and extension for a spring.
111
What is the independent variable in the experiment investigating force and extension?
Force, F
112
What is the dependent variable in the experiment investigating force and extension?
Extension, e
113
What is a control variable in the experiment investigating force and extension?
Spring constant, k
114
What is the initial step in setting up the apparatus for the spring experiment?
Set up the apparatus without any masses hanging from the spring.
115
What should be recorded after aligning the marker to a value on the ruler?
The initial length of the spring.
116
When a 100 g mass hanger is added, what must be recorded?
The mass (in kg) and position (in cm) from the ruler after the spring has extended.
117
What is the formula for calculating weight (W)?
W = mg, where W = weight in newtons (N), m = mass in kilograms (kg), g = gravitational field strength.
118
How is the force (F) added to the spring calculated?
F is calculated by multiplying the mass (in kg) by 10 N/kg.
119
What is the equation used to calculate the extension of the spring?
Extension = Final length - Original length.
120
What should be plotted to analyze the results of the spring experiment?
A graph of the force against extension.
121
What does it indicate if the force-extension graph has a linear region?
The force is proportional to the extension, and the spring obeys Hooke's law.
122
What type of errors should be considered when evaluating the experiment?
Systematic errors and random errors.
123
How can parallax error be avoided during measurement?
Ensure measurements on the ruler are taken at eye level.
124
What is a fiducial marker used for in the experiment?
To measure the extension more accurately.
125
What should be done before taking the reading for the new length of the spring?
Wait a few seconds for the spring to fully extend when a mass is added.
126
What happens if the spring is stretched past its limit of proportionality?
It will stop obeying Hooke's law.
127
What safety precautions should be taken during the experiment?
Wear goggles, stand up while carrying out the experiment, place a mat below the masses, and use a G clamp.
128
What common mistake should be avoided when calculating extension?
Calculating the increase in length each time instead of the total extension.
129
Fill in the blank: The extension measures how much the object has stretched by and can be found by subtracting the _______.
original length from each of the subsequent lengths.
130
What is a moment in physics?
The turning effect of a force about a pivot.
## Footnote
A moment can be calculated using the formula M = F × d, where M is the moment, F is the force, and d is the perpendicular distance from the pivot.
131
What does the equation M = F × d represent?
Moment = Force × Perpendicular distance from pivot.
## Footnote
M is in newton metres (Nm), F is in newtons (N), and d is in metres (m).
132
What is the principle of moments?
If an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment about that pivot.
## Footnote
This principle is crucial for understanding equilibrium in systems involving levers and beams.
133
What is a couple in terms of forces?
Two equal and opposite forces acting on an object that can cause rotation without passing through the same point.
## Footnote
This results in a net moment but no net force.
134
What is the significance of the distance from the pivot in a lever?
Increasing the distance from the pivot increases the moment and makes it easier to turn the object.
## Footnote
This is why handles are placed far from hinges on doors.
135
Fill in the blank: The units of a moment are _______.
Newton metres (N m) or Newton centimetres (N cm).
136
What happens when a smaller gear drives a larger gear?
The smaller gear rotates quicker than the larger gear but has a smaller moment.
## Footnote
This is typical in high gear settings on bikes or cars.
137
What is a lever?
A simple machine that increases the size of a force acting on an object to make it turn more easily.
## Footnote
Examples include bottle openers and crowbars.
138
True or False: A larger gear will rotate faster than a smaller gear when driven by it.
False.
139
What is the role of gears in mechanics?
Gears multiply the effect of a turning force using moments and consist of wheels with toothed edges that rotate on an axle.
## Footnote
The interaction of gear teeth allows for the transfer of motion between different shafts.
140
What type of forces cause moments on a horizontal beam?
Forces directed upwards or downwards.
## Footnote
These forces must be perpendicular to the distance from the pivot to create a moment.
141
How do levers and gears relate to the concept of moments?
Both systems utilize moments to transmit and amplify the rotational effects of forces.
142
What is the effect of applying a small force at a large distance from a pivot?
It can create a large moment, facilitating easier lifting or turning of an object.
143
What is the clockwise direction defined as?
The direction the hands of a clock move.
144
What is required for a see-saw to be balanced?
The total clockwise moments must equal the total anticlockwise moments around the pivot.
145
What is the formula for calculating the moment from a force?
Moment = Force × Distance from pivot.
146
What is pressure defined as?
The concentration of a force or the force per unit area
147
Why does a drawing pin push into a surface rather than upwards?
The sharp point is more concentrated, creating a larger pressure
148
How do large tyres on tractors affect pressure?
They spread the weight over a large area, reducing pressure and preventing sinking
149
What allows a nail to be hammered into a wall?
The sharp pointed end concentrates the force, creating a large pressure over a small area
150
What direction does the pressure exerted by a liquid create a force on an object?
At 90 degrees (at right angles) to the surface
151
What is the formula for calculating pressure?
Pressure = Force / Area
152
What units is pressure measured in?
Pascals (Pa)
153
True or False: High heels produce lower pressure on the ground compared to flat shoes.
False
154
What is the approximate atmospheric pressure at sea level?
About 100 kPa
155
How does atmospheric pressure vary with altitude?
It decreases as the height above sea level increases
156
What causes atmospheric pressure?
Air molecules colliding with a surface
157
What happens to the number of air molecules as altitude increases?
It decreases, leading to lower atmospheric pressure
158
In a liquid, what happens to pressure as depth increases?
Pressure increases with the height of the column of liquid above that point
159
What is the equation for calculating pressure in a liquid?
p = h × ρ × g
160
What do the variables in the equation p = h × ρ × g represent?
* p = pressure in pascals (Pa) * h = height of the column in metres (m) * ρ = density of the liquid in kg/m³ * g = gravitational field strength in N/kg
161
What is upthrust?
A force that pushes upwards on an object submerged in a fluid
162
What determines the size of upthrust on an object?
* The density of the fluid * The volume of fluid displaced
163
What happens if the upthrust on an object is equal to its weight?
The object will float
164
What is the relationship between an object's density and the fluid's density for it to float?
The object's density must be less than the density of the fluid
165
Fill in the blank: Atmospheric pressure decreases as the density of the _______ decreases.
molecules
166
What is the pressure at the bottom of a column of water compared to the top?
Higher
167
True or False: A polystyrene block will sink in water.
False
168
What happens to an iron block when placed in water?
It will sink
169
What is the density of water in g/cm³?
1.0 g/cm³
170
What is the density of a wooden block that causes it to float?
0.9 g/cm³
171
How does the pressure in a column of liquid affect the force exerted on an object submerged in it?
The pressure is exerted evenly across the whole surface of the object
172
What is distance?
Distance is a measure of how far an object travels.
## Footnote
It is a scalar quantity, meaning direction is not important.
173
What is displacement?
Displacement is a measure of how far something is from its starting position, along with its direction.
## Footnote
It is a vector quantity, describing both magnitude and direction.
174
What is speed?
Speed is the distance an object travels every second.
## Footnote
It is a scalar quantity.
175
What is the average speed formula?
Average speed = total distance / total time.
## Footnote
Distance is measured in metres (m) and time in seconds (s).
176
What is non-uniform motion?
Non-uniform motion refers to motion that is changing.
## Footnote
It can involve changes in speed, direction, or both.
177
What are typical speeds for a person walking?
Typical speeds for a person walking is about 1.5 m/s.
## Footnote
Factors affecting this include age, terrain, and fitness.
178
What is the speed of sound in air?
The speed of sound in air is approximately 330 m/s.
## Footnote
In seawater, it is around 1500 m/s.
179
What equipment can be used to measure speed?
Common equipment includes:
* A metre rule
* A timer
* A tape measure
* A trundle wheel.
## Footnote
Trundle wheels are ideal for measuring long distances.
180
How do light gates measure time?
Light gates measure time by starting a timer when an object passes through and stopping it when the object exits.
## Footnote
A flag on the object blocks light to trigger the timer.
181
What is the formula for calculating speed?
v = s / t, where v = speed (m/s), s = distance (m), t = time (s).
182
What is average speed for non-uniform motion?
Average speed = total distance / total time.
## Footnote
This accounts for variations in speed during the motion.
183
What is velocity?
Velocity is speed with a specified direction.
## Footnote
It is a vector quantity.
184
What distinguishes vector quantities from scalar quantities?
Vector quantities describe both magnitude and direction, while scalar quantities describe magnitude only.
## Footnote
Example of a vector: 40 N downwards; example of a scalar: 16° C.
185
What happens to velocity in circular motion?
In circular motion, the speed may be constant, but the velocity is always changing due to changing direction.
## Footnote
Example: The International Space Station moves at a constant speed but changes direction.
186
What does a straight line represent on a distance-time graph?
A straight line represents constant speed on a distance-time graph.
187
What does a curve indicate on a distance-time graph?
A curve indicates changing speed on a distance-time graph.
## Footnote
An increasing slope means acceleration, while a decreasing slope means deceleration.
188
What does a flat, horizontal line indicate on a distance-time graph?
A flat, horizontal line indicates that the object is stationary.
189
What does a straight line represent on a distance-time graph?
Constant speed
## Footnote
A straight line indicates that the object is moving at a constant speed.
190
How is changing speed represented on a distance-time graph?
By a curve
## Footnote
A curve indicates that the slope of the line is changing, representing acceleration or deceleration.
191
What does an increasing slope on a distance-time graph indicate?
The speed is increasing (accelerating)
## Footnote
An increasing slope means that the object is gaining speed.
192
What does a decreasing slope on a distance-time graph indicate?
The speed is decreasing (decelerating)
## Footnote
A decreasing slope means that the object is losing speed.
193
How long does Ose spend reading his book?
40 minutes
## Footnote
This is represented by the flat section of the line on the graph.
194
Which section represents Ose running home?
Section C
## Footnote
Section C has a steeper slope compared to Section A, indicating a larger speed.
195
What is the total distance travelled by Ose?
0.6 km
## Footnote
The total distance is determined by the final point on the distance axis.
196
What is the formula to calculate speed from a distance-time graph?
speed = gradient = ∆y/∆x
## Footnote
Where ∆y is the change in distance and ∆x is the change in time.
197
How is instantaneous speed determined from a distance-time graph?
By calculating the gradient of a tangent to the curve
## Footnote
The tangent touches the curve at a specific point to find speed at that moment.
198
What is acceleration defined as?
The rate of change of velocity
## Footnote
Acceleration describes how much velocity changes every second.
199
What is the formula for calculating average acceleration?
acceleration = ∆v/t
## Footnote
Where ∆v is the change in velocity and t is the time taken.
200
What does a positive acceleration indicate?
The object is speeding up
## Footnote
Positive acceleration means an increase in speed.
201
What does a negative acceleration indicate?
The object is slowing down (decelerating)
## Footnote
Negative acceleration shows a decrease in speed.
202
What is the gradient of a velocity-time graph used to calculate?
Acceleration
## Footnote
The gradient indicates how quickly the velocity changes.
203
What does a flat line on a velocity-time graph represent?
Constant velocity
## Footnote
A flat line indicates that there is no change in speed.
204
What does the area under a velocity-time graph represent?
Displacement (or distance travelled)
## Footnote
The area under the graph indicates how far the object has moved.
205
How is the area of a triangle under a velocity-time graph calculated?
Area = ½ × Base × Height
## Footnote
This formula is used when the area forms a triangle.
206
How is the area of a rectangle under a velocity-time graph calculated?
Area = Base × Height
## Footnote
This formula applies when the area forms a rectangle.
207
What is the significance of a steep slope on a velocity-time graph?
Indicates large acceleration (or deceleration)
## Footnote
A steep slope means that the object's speed changes very quickly.
208
What is the significance of a gentle slope on a velocity-time graph?
Indicates small acceleration (or deceleration)
## Footnote
A gentle slope means that the object's speed changes gradually.
209
What does the equation ∆v = v − u represent?
Change in velocity
## Footnote
Where v is the final velocity and u is the initial velocity.
210
How do you interpret a negative value for deceleration?
Indicates the object is slowing down
## Footnote
A negative acceleration value means the velocity is decreasing.
211
What is the first step in estimating distance from a velocity-time graph?
Identify whether distance can be determined exactly or by estimation
212
What does a curved velocity-time graph indicate about a train's movement?
The train is moving with changing acceleration
213
How is the area of each square on a velocity-time graph calculated?
Area = Base × Height
214
What is the area of a square with a base of 100 and height of 5?
500 m
215
How many squares were estimated to be under the curve in the example?
Approximately 17 squares
216
How is the total estimated distance calculated from the number of squares?
Total estimated distance = Number of squares × Distance represented by each square
217
What is the total estimated distance travelled if there are 17 squares each representing 500 m?
8500 m
218
What does the area under a velocity-time graph represent?
The distance travelled
219
How many enclosed areas are identified under the line in the car journey example?
Five enclosed areas
220
What is the area of a triangle with a base of 40 and height of 17.5?
350 m
221
What is the area of a rectangle with a base of 30 and height of 17.5?
525 m
222
What is the total distance travelled by the car if the areas are 350, 525, 75, 350, and 875?
2175 m
223
What equation applies to objects moving with uniform acceleration?
(final speed)² = (initial speed)² + 2 × acceleration × distance travelled
224
What does the variable 's' represent in the equation for uniform acceleration?
Distance travelled in metres (m)
225
What does the variable 'u' represent in the uniform acceleration equation?
Initial speed in metres per second (m/s)
226
What value does 'g' represent in freefall?
Acceleration due to gravity, approximately 9.8 m/s²
227
What happens when a skydiver reaches terminal velocity?
There is no longer any resultant force, and they travel at a constant speed
228
What forces act on a skydiver when they jump out of a plane?
* Weight (due to gravity) * Air resistance (due to friction)
229
What is the relationship between air resistance and the speed of a falling object?
The faster it falls, the larger the force of air resistance
230
Fill in the blank: The weight of an object is the force of ________ which acts on it.
gravity
231
Fill in the blank: When something falls, initially it ________.
accelerates
232
Fill in the blank: Eventually it falls at a steady speed when the force of friction equals the force of ________ acting on it.
gravity
233
What does the gradient of a velocity-time graph represent?
The acceleration of the object
234
What happens to the gradient of a velocity-time graph as an object reaches terminal velocity?
The gradient decreases from being very large down to zero
235
What occurs to a skydiver's speed when they open their parachute?
They experience a large deceleration due to a large resultant force upwards
236
What is the result of the air resistance being larger than the skydiver's weight when the parachute opens?
The skydiver decelerates
237
What does Newton's First Law of Motion state?
Objects will remain at rest, or move with a constant velocity unless acted on by a resultant force
## Footnote
This law implies that if the resultant force is zero, the object will maintain its state of motion.
238
What happens to an object at rest or moving with constant velocity if acted upon by a resultant force?
The object will change its state of motion
## Footnote
This change can either be a change in speed or direction.
239
What is inertia?
Inertia is the tendency of an object to resist changes in its state of motion
## Footnote
It is directly related to an object's mass.
240
What does Newton's Second Law of Motion state?
The acceleration of an object is proportional to the resultant force acting on it and inversely proportional to the object's mass
## Footnote
This can be expressed mathematically as F = ma.
241
In the equation F = ma, what does each variable represent?
* F = resultant force in Newtons (N)
* m = mass in kilograms (kg)
* a = acceleration in metres per second squared (m/s²)
## Footnote
This equation illustrates the relationship between force, mass, and acceleration.
242
How does the mass of an object affect its acceleration when a constant force is applied?
Acceleration is inversely proportional to mass
## Footnote
A larger mass results in smaller acceleration for the same force.
243
Fill in the blank: The Moon orbits the Earth at a constant speed of around _____ mph.
2000
## Footnote
However, because the Moon changes direction, it does not maintain a constant velocity.
244
Is it true that the resultant force is a vector quantity?
True
## Footnote
Resultant force has both magnitude and direction.
245
What is the effect of balanced forces on an object's motion?
The object will maintain a constant velocity
## Footnote
Balanced forces result in zero resultant force.
246
What is the aim of the required practical investigating force and acceleration?
To investigate the effect of varying force on the acceleration of an object of constant mass
## Footnote
This experiment helps demonstrate Newton's second law.
247
What are the control variables in the experiment investigating the effect of mass on acceleration?
Force, F
## Footnote
The force applied must remain constant to observe the effect of changing mass.
248
What safety consideration should be taken during the experiments?
Don't stand directly beneath the weight hanger
## Footnote
This precaution prevents injury in case weights fall.
249
What is the expected outcome when varying the force on an object of constant mass?
The acceleration of the object will increase as the force increases
## Footnote
This relationship is a direct application of Newton's second law.
250
What should be done to minimize random errors in timing during experiments?
Take repeat readings and calculate an average
## Footnote
This helps increase the reliability of the results.
251
Fill in the blank: The equation for calculating acceleration is _____ = change in velocity / time.
a
## Footnote
This equation is derived from rearranging Newton's second law.
252
Explain the significance of the negative sign in resultant force calculations.
It indicates that the resultant force acts in the opposite direction to the object's motion
## Footnote
This often indicates deceleration.
253
What does Newton's third law of motion state?
Whenever two bodies interact, the forces they exert on each other are equal and opposite.
254
What principle explains that all forces arise in pairs?
If object A exerts a force on object B, then object B exerts an equal and opposite force on object A.
255
What type of forces do force pairs consist of in Newton's third law?
Force pairs are of the same type.
256
How does Newton's third law relate to walking?
The foot pushes the ground backwards, and the ground pushes the foot forwards.
257
In the context of Newton's laws, what is a free body force diagram used for?
To illustrate the forces acting on an object.
258
What does Newton's first law of motion state?
Objects will remain at rest, or move with a constant velocity unless acted on by a resultant force.
259
What are the conditions for identifying Newton's third law?
Pairs of equal and opposite forces acting on two different objects.
260
Why is the free body force diagram of a book on a table an example of Newton's first law?
The forces acting on it are balanced, meaning there is no resultant force.
261
What is inertia?
The tendency of an object to continue in its state of rest, or in uniform motion unless acted upon by an external force.
262
How is inertial mass defined?
The ratio between the force applied to an object and the acceleration it experiences.
263
What is the formula for calculating inertial mass?
inertial mass = force / acceleration.
264
What does it mean if an object has a larger inertial mass?
It will experience smaller accelerations for the same applied force.
265
Fill in the blank: Inertial mass is _____ proportional to acceleration.
inversely
266
If three objects are subjected to the same force and have different accelerations, how can you determine which has the largest inertial mass?
The object with the smallest acceleration has the largest inertial mass.
267
What is the relationship between inertial mass and Newton's second law?
The definition of inertial mass is similar to Newton's second law, as calculating mass involves force and acceleration.
268
What is the definition of stopping distance?
The total distance travelled during the time it takes for a car to stop in response to some emergency.
269
What is the equation for stopping distance?
Stopping distance = Thinking distance + Braking distance.
270
What is thinking distance?
The distance travelled in the time it takes the driver to react (reaction time) in metres (m).
271
What is braking distance?
The distance travelled under the braking force in metres (m).
272
How does speed affect stopping distance?
For a given braking force, the greater the speed of the vehicle, the greater the stopping distance.
273
At a speed of 20 m/s, what was the stopping distance in the worked example?
40 metres.
274
In the worked example, what was the thinking distance?
14 metres.
275
What is the braking distance calculated in the worked example?
26 metres.
276
What happens to the vehicle's velocity during the reaction time before braking?
The vehicle continues moving at a constant velocity.
277
What does the area under the velocity-time graph during the reaction time represent?
The thinking distance.
278
What does the area under the velocity-time graph during braking represent?
The braking distance.
279
What is the typical range of human reaction time for someone who is alert?
0.2 - 0.9 seconds.
280
How can human reaction time be measured simply?
By dropping a ruler and measuring the distance it falls before being caught.
281
What factors can increase thinking distance?
* Tiredness
* Distractions (e.g. using a mobile phone)
* Intoxication (i.e. consumption of alcohol or drugs)
282
What is the relationship between thinking distance and speed?
Thinking distance is directly proportional to the speed of the car.
283
What are the main factors affecting braking distance?
* Speed of the car
* Vehicle condition (e.g. worn tyres)
* Road condition (e.g. wet or icy roads)
* Vehicle mass (e.g. heavy vehicles take longer to stop)
284
What happens to the kinetic energy of a car when brakes are applied?
The kinetic energy decreases and the thermal energy of the brakes increases.
285
What is the formula for work done by the braking force?
Work done = Force × distance travelled.
286
In the worked example, how much work is done by the braking force to stop the car?
168,750 J.
287
What is the braking distance calculated in the worked example with a braking force of 6000 N?
28.1 m.
288
How is braking distance affected by speed?
The braking distance is proportional to the speed squared (if the speed is doubled, the distance increases 4 times).
289
True or False: The braking distance is directly proportional to the vehicle's speed.
False.
290
What common mistake should be avoided when discussing why brake temperature increases?
Writing about the friction between the wheels and the road instead of the friction between the brakes and the wheels.
291
What is the equation for calculating momentum?
p = mv
## Footnote
Where p = momentum in kg m/s, m = mass in kg, and v = velocity in m/s.
292
What is the unit of momentum?
kilogram metre per second (kg m/s)
## Footnote
Momentum is a product of mass and velocity.
293
When does an object have no momentum?
When it is at rest (i.e v = 0)
## Footnote
Momentum is dependent on the object's velocity.
294
What happens to the momentum of an object if it accelerates or decelerates?
The momentum changes
## Footnote
Momentum can also change if the object's direction or mass changes.
295
True or False: Momentum can be either positive or negative.
True
## Footnote
The direction of travel affects the sign of momentum.
296
What does the principle of conservation of momentum state?
In a closed system, the total momentum before an event is equal to the total momentum after the event
## Footnote
A closed system has no external forces acting on it.
297
What is a closed system in terms of momentum?
A system with constant energy and absence of external forces
## Footnote
Examples of external forces include friction.
298
What happens to the overall momentum of two objects moving in opposite directions at the same speed?
The overall momentum is 0
## Footnote
Their momenta cancel each other out.
299
What is the total momentum of a system before a collision if one mass is moving and another is at rest?
It is equal to the momentum of the moving mass
## Footnote
The resting mass contributes 0 to the total momentum.
300
What is an elastic collision?
A collision where objects collide and move in opposite directions
## Footnote
Kinetic energy is conserved in elastic collisions.
301
What is an inelastic collision?
A collision where objects stick together and move in the same direction
## Footnote
Kinetic energy is not conserved in inelastic collisions.
302
What is the formula for calculating force in relation to momentum?
Force = rate of change of momentum
## Footnote
Δt is the change in time for the momentum change.
303
Fill in the blank: The force of an impact in a vehicle collision can be decreased by increasing the _______.
contact time
## Footnote
Longer contact time reduces the force experienced.
304
What are the main vehicle safety features designed to absorb energy upon impact?
* Crumple zones
* Seat belts
* Airbags
## Footnote
These features help increase the time taken for the change in momentum.
305
How do seat belts contribute to safety in vehicles?
They keep passengers fixed to their seat and stretch slightly to increase contact time
## Footnote
This reduces the force on passengers during a collision.
306
What role do airbags play in vehicle safety?
They act as a soft cushion to prevent injury during a collision
## Footnote
Airbags deploy upon impact to slow down the passenger's motion.
307
What is the purpose of crumple zones in vehicles?
To crush or crumple in a controlled way during a collision
## Footnote
This increases the time over which the vehicle comes to rest.
308
What is the function of crash mats in gymnasiums?
To reduce the risk of injury by absorbing the force of a fall
## Footnote
They create a longer contact time during impact.
309
True or False: Safety features can completely prevent injuries in all cases.
False
## Footnote
Safety features reduce the chance of serious injury but do not eliminate it.
310
What factors affect the usefulness of safety equipment during a collision?
* Mass
* Velocity
## Footnote
Larger mass and higher velocity lead to greater momentum and force.
