P5:Forces Flashcards
1
Q
What do vector quantities have
A
•Magnitude •Direction
2
Q
Physical quantities of vectors include …
A
•force•velocity•displacement•acceleration•momentum
3
Q
What is a scalar quantity
A
A physical quantity that only contains magnitude and NOT DIRECTION
4
Q
Scalar quantities include…
A
•Speed•Distance •Mass•Temperature •Time
5
Q
What usually represents a vector, and what does this symbol show
A
Usually represented by an arrow •length of arrow represents magnitude •direction of arrow represents the direction of the quantity
6
Q
Forces can be…
A
•contact (when to objects have to be touching for a force to act) E.G:friction, air resistance OR•non-contact (when an object doesn’t need to be touching for a force to act) E.G:magnetic force, gravitational force
7
Q
A force is a…
A
Push or pull on an object that is caused by it interacting with something
8
Q
When two objects interact…
A
There is a force produced on both sides
9
Q
Define the term ‘interaction pair’
A
A pair of forces that are equal and opposite and act on two interacting objects
10
Q
Gravitational force is…
A
The force of attraction between masses
11
Q
What are gravity’s two main important effects
A
•on the surface of the planet, it makes all things fall towards the ground AND•it gives everything a weight
12
Q
Define the term ‘mass’
A
The amount of of ‘stuff’ in an object
13
Q
What is weight
A
Weight is the force acting on an object due to gravity.Close to the earth, this force is caused by the gravitational field around the eating
14
Q
Gravitational field strength varies, where is it strongest
A
It’s stronger the closer you are to the mass and it’s stronger for larger masses
15
Q
What does the weight of an object depend on?
A
The strength of a gravitational force at the location of the object. This means the weight of an object changes with location
16
Q
Weight is measured in …
A
Newtons
17
Q
What is the term to describe the weight force acting from a single point on an object
A
‘Centre of mass’
18
Q
Weight is measured using…
A
A calibrated spring balance or newtonmeter
19
Q
Mass and weight are directly proportional. What equation would you use to work out the weight of an object?
A
Weight(N)=Mass(KG) x Gravitational Field Strength(N/KG)
20
Q
Increasing the mass of an object increases his weight. Write this using the direct proportional symbol
A
W ∝ M
21
Q
What can you use to show the forces acting on an object
A
A free body diagram
22
Q
What do the things on a free body diagram represent
A
•The size of the arrows show the relative magnitudes of the forces •The direction show the direction of forces acting on the object
23
Q
A resultant force is…
A
The overall force on a point or object
24
Q
How many forces act on an object along any direction
A
At least two
25
If you have a number of forces acting at a singles point what can you replace them with
A single force AKA: the resultant force
26
If the forces all act along a parallel line, how is the overall effect found ...
By adding those going in the same direction and subtracting any force going in the opposite direction
27
If w resultant force moves an object through a distance...
Energy is transferred & work is done
28
To make something move...
A force must be applied
29
The thing applying the force needs...
A source of energy E.G:food or fuel
30
Work is done even if the energy transferred is ...
Useful or wasted
31
Equation for work done
Work Done(J)=Force(N) x Distance(m) W=FxS
32
One joule of work is done when a force of...
One newton caused an object to move a distance of one metre.
33
Conversion of joules to newton meters
1J = 1Nm
34
How to use a scale drawing to find a resultant force
1.Draw all the forces acting on an object, to scale ‘tip-to-tail’2.Draw a straight line from the start of the first force to the end of the last force (resultant force)3.Measure length of resultant force on the diagram to find the magnitude, angle and direction of the force
35
If all the forces acting on an object combine to give a resultant force of zero Or If the forces are balanced
The object is at an equilibrium
36
For three forces the scale diagram should...
Form a triangle
37
To draw an equilibrium the tip of the last force...
Should end where the tail of the first force you drew began
38
If told to find the missing force when an object is at equilibrium, you should
•draw out the forces you do know•join the end of the last force to the start of the first force•^ this line is the missing force so you can measure its size and direction
39
Not all forces act...
Horizontally or vertically, some are at awkward angles
40
If you find a force with an awkward angle...
•split it into two components at right angles (acting together these components have the same effect as the single force)
41
To resolve an single force...
•split it into components by drawing it on a grid •draw the force to scale•add horizontal and vertical components along grid lines •Then measure the components
42
When you apply a force to an object you may cause it to...
Stretch, compress or bend ^these actions transfer energy
43
If an object is being stretched, compressed or bent you need...
More than one force acting on the object otherwise the object would simply move in the direction of the applied force
44
An object has been elastically deformed if...
It can go back to its original shape and length after the force has been removed. They are called elastic objects E.G: a spring
45
An object has been inelastically deformed if...
It doesn’t return to its original shape and length after the force has been removed
46
Work is done when a forced stretches or compressed an object because...
Energy is transferred to the elastic potential energy store of the object
47
If work is done in an elastically deformed object...
ALL energy is transferred to the objects elastic potential energy store
48
Extension is directly proportionately to force
F ∝ e This is the equation:F(N)=K(N/m) x e(m)
49
The spring constant depends on...
The material that you are stretching•a stiffer spring has a greater spring constant
50
The F=Ke equation also works for compression...
Where e is just the difference between the natural and compressed lengths (The compression)
51
There is a limit to the amount of force you can apply to an object...
To keep on increasing it proportionally
52
Distance is just how far an object has moved its has...
A scalar quantity
53
Displacement measures the distance and direction in w straight line from an objects starting point to its finishing point
It is a vector quantity E.G: a bearing
54
EXAMPLE:If you walk 5m north and 5m south...
Your displacement is 0 But the distance travelled is 10m
55
Speed and velocity both measure how fast you’re going, but...
•Speed is a scalar quantity •velocity is a vector quantity
56
you can have objects travelling at a constant speed with a changing velocity
When an object is changing direction whilst staying at the same speed E.G:a car going round a roundabout
57
If you want to measure the speed of an object moving with a constant speed you should...
Time how long it takes the object to travel a certain distance
58
The equation for measure an objects speed
Speed(m/s)= distance travelled(m) / time(s)V= m/s
59
Objects rarely travel at a constant speed, your speed is always changing...
The formula:V=s / tGives the average (mean) speed during that time period
60
A persons walking speed...
1.5m/s•many things can effect this, for example a persons fitness,age, distance travelled or the terrain
61
A persons running speed
3m/s•many things can effect this, for example a persons fitness,age, distance travelled or the terrain
62
A persons cycling speed
6m/s
63
A cars speed
25m/s
64
A trains speed
30m/s
65
A planes speed
250m/s
66
The speed of sound (330m/s in the air) changes depending on...
What the sound waves are travelling through, the speed of the wind
67
Wind speed can be affected by things like
•Temperature •atmospheric pressure •buildings in that area Or•structures near by
68
Acceleration is...
How quickly you’re speeding up, it is the change in velocity in a certain amount of time
69
Equation for acceleration
Acceleration (m/s {squared}) =
70
Uniform acceleration means...
A constant acceleration
71
Acceleration due to gravity is uniform for objects in free fall.
It’s roughly equally to 9.8m/s² bear the earths surface and has the same value as gravitational field strength
72
Equation for uniform acceleration
V² - U²= 2asFinal velocity(m/s) - initial velocity(m/s) = acceleration(m/s²) x distance (m)
73
To estimate an acceleration...
Use the typical speed of the object and ÷ by the time
74
Use distance time graphs to show...
An object moving on a straight line
75
Gradient = speed
The steeper the graph, the faster the speed
76
DTG:Flat sections
Stationary
77
DTG:Straight uphill
Travelling at a steady speed
78
DTG:Curve
Acceleration or deceleration
79
DTG:Steepening curve
Speeding up
80
DTG:Levelling off curve
Slowing down
81
Velocity time graphs show...
How an objects velocity changes
82
VTG:Gradient
Acceleration
83
VTG:Flat section
Steady speed
84
VTG:Steeper gradient
Greater acceleration or deceleration
85
VTG:Uphill sections (/)
Acceleration
86
VTG:Downhill sections(\)
Deceleration
87
VTG:A curve
Change in acceleration
88
The area under any section of the graph is...
Equal to the distance travelled in that time interval
89
If the graph is curved...
Use a tangent to the curve at a point to find the acceleration
90
If an object has no force propelling it along he will always...
Slow down and stop because of friction
91
Friction always acts in...
The opposite direction to movement
92
To travel at a stress speed...
The driving forces need to balance the frictional forces
93
You get friction between two surfaces in contact...
Or when an object passes through fluid (this is also know as drag)
94
You can reduce friction between surface by using...
Lubricant
95
Drag is the resistance you get in a...
Fluid (a gas or a liquid)•Air resistance is a type of drag
96
The most important factor by far in reducing drag is...
Keeping the shape of the object streamlined (This is where the object is designed to allow fluid to flow easily across it, reducing drag)
97
Parachutes work in the opposite way...
They want as much drag as they can get
98
Frictional Forces from fluids always...
Increase with speed(E.G: a car has much more friction to work against when travelling at 70mph compared to 30mph)
99
When a falling object first sets off, the force of gravity is much more...
Than the frictional force slowing it down, so it accelerates
100
When an object is falling, as the speed increases...
•The friction builds up, this gradually reduces the acceleration •Eventually the frictional force is equal to the accelerating force •The resultant force is zero •It will have reached its maximum speed or terminal velocity and will fall at a steady speed
101
Typically, the less streamlined an object is...
The lower it’s terminal velocity
102
Objects with a large surface area...
Tend to have lower terminal velocity as there is more air resistance acting on it at any given speed
103
Terminal velocity depends on shape and area
For example, if you dropped a marble and a beach ball off a tall building, the marbles terminal velocity would be higher than the terminal velocity of the beach ball.The beach ball spends less time accelerating before the air resistance is large enough to equal the accelerating force
104
Newton’s first law
A resultant force is needed to make something start moving, speed up or slow down •if the resultant force on a stationary object is zero, the object will stay stationary•if the resultant force on a moving object is zero, it will just carry on moving at the same velocity
105
A non zero resultant force will always...
Produce an acceleration or deceleration in the direction of the force •On a free body diagram, the arrows will always be unequal
106
Five different forms acceleration can take
•Starting•Stopping•Speeding up•Slowing down •Changing direction
107
Acceleration is proportional to the resultant force
F ∝ a
108
Acceleration is also...
Inversely proportional to the mass of the object
109
Newton’s second law
F= m aResultant force (N) = Mass(Kg) x Acceleration(m/s²)
110
To estimate the acceleration
Use the typical speed of an object and multiply it by the mass
111
Inertia is...
The tendency for motion to remain unchanged
112
An objects inertial mass measures how...
Difficult it is to change the velocity of an object
113
Inertial mass can be found using Newton’s second law
m= F ÷ a•inertial mass is just the ratio of a force over acceleration
114
Newton’s third law
When two objects interact, the forces the exert on each other are Raquel and opposite E.G:If you push a trolley, the trolley will push back against you just as hard & when you stop pushing, so does the trolley
115
An example of Newton’s third law is...
An equilibrium situation, but if the two forces are different types and not acting on the force this isn’t an example of Newton’s third law
116
In an emergency, a driver may perform an emergency stop...
This is where maximum force is applied by the brakes in order to stop the car in the shortest possible distance
117
The longer it takes to perform an emergency stop...
The higher the risk of crashing into what ever is infront if you
118
Distance it takes for a car to stop in an emergency is found by...
Stopping distance = thinking distance + braking distance
119
Thinking distance
How far the car travels during the drivers reaction time
120
Braking distance
The distance taken to stop under the braking force (once brakes are applied)
121
Breaking distance if a car is travelling at 30mph
14m
122
Breaking distance if a car is travelling at 60mph
55m
123
Breaking distance if a car is travelling at 70mph
70m
124
Thinking distance is affected by
•your speed - the faster you’re going the further you’ll travel during the time it takes you to react•your reaction time - the longer your reaction time, the longer you thinking distance
125
Braking distance is affected by...
•Your speed - for a given braking force, the faster a vehicle travels, the longer it takes to stop•Weather or road surface - if it’s wet or icy, or there are leaves or oil on the road, there is less grip(so less friction), can causes tyres to skid •Condition of tyres - if bald, they can’t get rid of water in wet conditions = skidding•How good your brakes are - if worn or faulty, they won’t apply as much force
126
When the brake is pushed, this causes brake pads to be pressed onto the wheels...
Contact force = friction, which causes work to be done.
127
The work done between the brakes and the wheels transfer energy from the kinetic energy stores of the wheels...
To the thermal energy stores of the brakes. The brakes increase in temperature.
128
The faster a vehicle is going, the more energy it has in its kinetic stores...
So the more work needs to be done to stop it. This means that the greater braking force is needed to make it stop within a certain distance
129
A larger braking force means...
A larger deceleration
130
Very large deceleration can be dangerous because...
They may cause brakes to overheat (they don’t work as well) or could cause the vehicle to skid
131
Estimate the forces involved in accelerations if vehicles by...
Using typical values
132
Momentum(kg m/s)...
Mass(kg)x velocity(m/s) P=m x v
133
Momentum is...
A property that all moving objects have
134
The greater the mass of an object, or the greater its velocity...
The more momentum the object has
135
In a closed system the total momentum before an event (e.g a collision)...
Is the same after the event. This is called conservation of momentum
136
A closed system...
Is the fancy was of saying that no external forces act
137
If the momentum before an event is zero, the momentum after will be zero...
E.G:In an explosion, the momentum before is zero. After the explosion, the pieces fly off in different directions, so that the total momentum cancels out to zero
138
A moving car hits into the back of a parked car. The crash causes the two cars to lock together, and they continue moving in the direction that the original moving car was travelling at, but at a lower velocity...
Before: The momentum was equal to mass of moving car x it’s velocity After: The mass of the moving object has increased, but it’s momentum is equal to the momentum before the collision. So an increase in mass causes a decrease in velocity
