P5 Flashcards
1
Q
What is a vector quantity?
A
A quantity that has magnitude and direction.
2
Q
What are 5 examples of vector quantities?
A
- Displacement. 2. Velocity. 3. Acceleration. 4. Force. 5. Momentum
3
Q
What is a scalar quantity?
A
A quantity that has only magnitude.
4
Q
What are 4 examples of scalar quantities?
A
- Speed. 2. Direction. 3. Time. 4. Temperature.
5
Q
What is a contact force?
A
A force that is exerted only when two objects are touching.
6
Q
What is a non contact force?
A
A force that one object can apply to another object without touching it.
7
Q
What are 4 examples of contact forces?
A
- Friction. 2. Air resistance. 3. Tension. 4. Normal contact force.
8
Q
What are 3 examples of non contact forces?
A
- Gravitational force. 2. Electrostatic force. 3. Magnetic force.
9
Q
What’s Earth’s gravitational field strength?
A
9.8 N/kg
10
Q
What is weight?
A
The force exerted on an object due to gravity.
11
Q
Difference between weight and mass
A
Mass is the amount of matter in an object while weight is the measure of the gravitational pull on an object. Weight varies with gravitational field strength while mass remains the same.
12
Q
Weight equation
A
Mass (kg) x gravitational field strength (N/kg) = weight (N)
13
Q
What is the centre of mass?
A
The point of an object at which the entire mass of the object appears to act from.
14
Q
What is weight measured with?
A
Calibrated spring - balance (newtonmeter)
15
Q
What is the resultant force?
A
The overall force on a point or object
16
Q
What does a free body diagram show?
A
A diagram showing all of the forces acting on an object.
17
Q
What is work done?
A
The energy transferred into an object by applying a force
18
Q
Work done equation
A
Force (N) x distance (m) = work done (j)
19
Q
How many newton - metres is 1 joule?
A
1Nm (for moments)
20
Q
What is elastic potential energy?
A
The potential for an object to be compressed, bent or stretched
21
Q
What is an elastically deformed object?
A
An object that can return to its original length and shape after all the forces have been removed e.g. spring.
22
Q
What is an inelastically deformed object?
A
An object that doesn’t return to its original shape and length after all the forces have been removed.
23
Q
What is the limit of proportionality?
A
The point at which extension is no longer directly proportional to the force applied.
24
Q
Force equation
A
Spring constant (N/M) x extension (M) = force (N)
25
What is a spring constant?
The object's resistance to being stretched
26
If there's a higher spring constant what does that mean for the energy needed to stretch or compress it?
It needs more energy to stretch or compress it as a high spring constant means it is very stiff.
27
What is the energy like in a spring?
When a force stretches or compresses a spring; the spring does work and elastic potential energy is stored. The work done and elastic potential energy should be equal if it's not inelastically deformed.
28
How do you calculate elastic potential energy?
0.5 x spring constant (N/m) x extension (m) ∧2
29
Required practical 6 - spring (7)
1. Set up equipment. 2. Attach pointer thing to the bottom of the spring. 3. Ruler should be perpendicular to this. 4. Measure initial length without any weights. 5. Add 10g masses to the bottom and measure lengths. 6. Work out the extension by subtracting new length by old length. 7. Convert to weights by multiplying by 9.8 and plot a graph.
30
What are some forces which cause rotation? (3)
1. Pushing on a door handle. 2. Using a spanner. 3. Turning a tap.
31
What is a moment?
The turning effect of a force
32
What's the equation for a moment of a force?
Force (N) x distance (perpendicular from the pivot) (m) = moment (Nm)
33
If an object is balanced what should be equal?
Total clockwise moment = total anticlockwise moment.
34
What happens if you increase the distance from the pivot?
Less force is needed to get the same movement
35
What happens if you have a bigger gear?
Transmits a bigger movement but turns slower.
36
What is a fluid?
A substance that can flow (liquid and gases)
37
What do collisions in fluids cause?
Lots of frequent and successful collision on the walls which exert a normal force (which is perpendicular to the walls).
38
How can pressure be calculated?
Force normal (N) ÷ Area (m²) =pressure (Pa)
39
How do particles cause pressure?
As particles move about within they a substance they collide with each other and the sides of the containers. This transfers energy and exerts a force. The amount of force per unit area is known as pressure
40
What is density?
The measure of how compact a substance is. The number of particles per unit area
41
Pressure in a fluid equation
Height of the column (m) X gravitational field strength (N/Kg) X density of the fluid (kg/m∧3)
42
Why, in a liquid, does the pressure at a point increase with the height of the column of liquid above that point and with the density of the liquid?
The deeper you go in a liquid; the greater the weight of the liquid above pushing down and the greater the pressure. A denser liquid also has a greater weight for the same volume, leading to higher pressure at the same depth. Always link to force / area = pressure.
43
What is upthrust?
When a partially or totally submerged object has a larger pressure on the bottom surface than the top. The resultant force upwards is upthrust.
44
An objects floats if...
The objects weight = upthrust. (Object is less dense than the fluid)
45
An object sinks if...
The objects weight is larger than the upthrust (more dense than the fluid).
46
What is the atmosphere?
Thin layer of air around Earth. It gets less dense with increasing altitude.
47
How does atmospheric pressure vary different altitudes?
The number of air molecules (aka the weight of the air) decreases when the height increases. So the pressure decreases.
48
What is distance?
How far an object moves. Scalar.
49
What is displacement?
How far an object has moved in a given direction. Vector. For example someone could walk around a garden and their distance could be 10m but their displacement could be 0 if they ended up in the same place.
50
What is speed?
How fast you're going. Doesn't involve direction so is scalar
51
What is velocity?
How fast you're going in a given direction. This means it's possible to have a constant speed but a changing velocity
52
1.5 m/s
Average walking speed
53
3 m/s
Average running speed
54
6 m/s
Average cycling speed
55
25 m/s
Average car speed
56
55 m/s
Average train speed
57
250 m/s
Average plane speed
58
330 m/s
Speed of sound
59
300,000,000 m/s
Speed of light
60
What is the equation for distance?
distance (m) = speed (m/s) x time (s)
61
Uniform acceleration equation
Final velocity (m/s)² - Initial velocity² = 2 x acceleration (m/s∧2) x distance (m)
62
Acceleration equation
Change in velocity (m/s) ÷ time (s) = acceleration (m/s∧2)
63
If an object moves along a straight line then what kind of graph can the distance travelled be represented on?
Distance - time graph.
64
What does each line mean on a distance time graph?
Flat line → stopped. Steep line → fast constant speed. Gradient → speed
65
What does each line mean on a velocity time graph?
Flat line → constant speed. Steep line → acceleration. Distance = area under line.
66
What is terminal velocity?
The greatest velocity a falling object can reach.
67
What is friction?
The resistance between two touching objects
68
What are the rules of friction?
1. If an object has no force propelling it then it will slow down. 2. Friction acts in the opposite direction of movement. 3. To travel at a steady speed the driving force must balance friction.
69
What is drag?
The resistance an object experiences when passing through a fluid e.g. swimming pool.
70
Rules of drag
1. The more streamlined an object is the lower the force of drag. 2. Drag increases with increasing speed
71
What is reaching terminal velocity?
When the frictional forces matches the accelerating forces so the resultant force is zero.
72
What is air resistance?
A from of drag experienced by objects in atmosphere due to air particles.
73
What does Newton's first law state?
An object at rest stays at rest, an object in motion stays in motion (same velocity).
74
What is inertia?
The tendency of an object to continue in their state of rest or motion.
75
What does Newton's second law state?
Acceleration is directly proportional to the resultant force. F = ma
76
Required practical 7 - investigating force and acceleration
1. Attach the car to the string at one end, with the other end running across the bench pulley. 2. Attach the weight stand to the loose end of string. 3. Release the weight stand (allowing it to fall) and begin the timer. 4. Stop timing when the car hits the pulley at the other end of the bench. To Investigate Changing Force on a Constant Mass: A. Add a 10g mass to the weight stack. B. Release the weights and time the car travelling across the bench. C. Repeat the experiment by adding 10g weights and recording the time for each. To Investigate Changing Mass with a Constant Force: A. Attach a 10g mass on top of the toy car. B. Pull the car back to the starting chalk line. C. Release the car and time how long it takes for the car to travel across the bench.
77
What does Newton's third law state?
When two objects interact, the forces they exert on each other are equal in size and opposite in direction
78
Effect of applying a force on an object
The object pushes back with an equal force in the opposite direction
79
Equilibrium
A state in which opposing forces or influences are balanced.
80
Hooke's law
Extension is directly proportional to force until the spring reaches it's elastic limit
81
Stopping distance
The total distance a vehicle travels during both thinking and braking distance
82
Thinking distance
The distance travelled by the vehicle in the time it takes the driver to react
83
Braking distance
The distance a car travels from the time the driver applies the brakes until the car comes to a complete stop
84
14m
Average car braking distance at 30 mph
85
55m
Average car braking distance at 60 mph
86
75m
Average car braking distance at 70 mph
87
Factors affecting thinking distance (3)
1. Reaction times. 2. Influence of alcohol / drugs. 3. Tiredness.
88
Factors affecting braking distance
1. Speed. 2. Weather and road surface. 3. Condition of tyres. 4. Condition of brakes
89
0.2-0.9 s
Typical reaction times
90
Ruler drop test
Test for reaction times
91
What about the energy when breaking?
When a force is applied to the brakes of vehicle, work done by the friction force between the brakes and the wheel reduces kinetic energy of the vehicle and the temperature of the brakes increases.
92
What may large decelerations lead to?
Dangerous like the brakes overheating or loss of control.
93
Momentum (Nm)
Mass (m) x velocity (m/s)
94
Closed system
A system in which no matter is allowed to enter or leave
95
Conservation of momentum
The idea that the total momentum before an event (e.g. a collision) will equal the total momentum after the event
96
Newton's cradle
A device that demonstrates the conservation of momentum.
97
Safety features on cars
1. Crumple zones. 2. Seat belts. 3. Air bags
