Forces & Motion Flashcards
(90 cards)
1
Q
Speed Formula
A
S = d/t
2
Q
Speed measurement
A
M/s
3
Q
Difference between velocity and speed
A
Velocity is speed but has a given direction. You can have objects travelling at a constant speed with changing velocity.
4
Q
Acceleration definition
A
The change in velocity per unit time
5
Q
Acceleration unit
A
M/s^2
6
Q
Acceleration word formula
A
Acceleration = change in velocity ➗ time taken
7
Q
Acceleration letter formula
A
(V-u) ➗(a x t)
8
Q
What do you call negative acceleration?
A
Deceleration. Object is slowing down.
9
Q
If a curve is getting steeper is it acceleration or deceleration?
A
Acceleration
10
Q
What is weight?
A
A gravitational force measured in newtons
11
Q
On earth what is the weight of an object?
A
The gravitational force pulling it towards the centre of the earth.
12
Q
Is it the mass or weight that changes on the moon?
A
Weight. Mass is always the same.
13
Q
How do you compare the weight of two objects?
A
Using a balance. The object with the greater weight will have the greater mass.
14
Q
Weight word formula
A
Weight 🟰 mass ✖️ gravitational field strength
15
Q
Weight equation letter formula
A
W 🟰mg
16
Q
Weight unit
A
N
17
Q
Gravity on Earth
A
10N/kg
18
Q
Gravity on moon
A
1.6N/kg
19
Q
What is density?
A
A measure of the compactness of a substance. Substance mass per unit volume.
20
Q
Density word formula
A
Density 🟰 mass ➗ volume
21
Q
Density letter formula
A
Rho = m ➗ V
22
Q
Density unit
A
kg/m^3
23
Q
Density depends on the ___ of an object
A
Material
24
Q
If the density is lower than the fluid will an object float or sink?
A
Float
25
An object sink in a fluid. what does that mean about its density?
It is more dense than the fluid
26
How to find the density of an irregularly shaped solid?
Use a Eureka can and a measuring cylinder and measure the displacement of water when the solid object is dropped into the can. That is its volume. Divide by mass measured on balance.
27
How to measure the density of a regular object
Use a ruler to measure width, height, length. That is your volume. Measure mass using balance.
28
What is the resultant force?
The overall force and appoint or object. The single force that has the same effect as all the forces acting at a single point.
29
If the forces are all parallel, how do you find the overall effect?
By adding all those in the same direction and subtracting those in the opposite direction
30
Are Forces vectors or scalars?
Vectors
31
What is a vector? name examples.
Quantities with a magnitude and direction. E.G force, velocity, acceleration, momentum.
32
What is a scalar? Name examples.
Quantities that have magnitude only and no direction. E.G speed, distance, mass, temperature, time.
33
Can a force change motion?
Yes
34
What are the five ways that are forced can change motion?
1. Start moving.
2. Stop moving.
3. Speed up.
4. Slowdown.
5. Change direction.
35
True or false? If the forces cancel each other out the motion changes.
False, the motion won’t change
36
What happens if there is no resultant force on a stationary object?
The object will remain at rest
37
What happens if there is no resultant force on a moving object?
The object will continue moving at a constant speed in a straight line
38
What is the relation of acceleration to resultant force?
Direct proportion
39
What does a resultant force always produce?
Acceleration in the direction of the force
40
What is the relation of acceleration to the mass of an object?
Inverse proportion. An object with larger mass will accelerate less.
41
Force and acceleration formula
F = ma
42
What causes circular motion?
A perpendicular force called centripetal force
43
If an object is travelling in circular orbit, what is it constantly doing?
constantly changing direction so constantly changing velocity so constantly accelerating
44
What is friction?
A force between two objects that are in contact and are moving or trying to move relative to each other. Friction always acts in the opposite direction to movement.
45
What does friction always result in and why?
Heating because some kinetic energy is transferred to the object and its surroundings as thermal energy as the object slows down
46
Air Resistance is a form of what?
Friction
47
If an object is moving faster, what happens to the air resistance?
It is greater
48
Why do falling objects accelerate when first setting off?
Because the force of gravity is much greater than the air resistance. The downwards force is greater than the upward force.
49
Why is terminal velocity reached when an object falls?
Because as the speed increases the air resistance also does, and therefore the resultant force downwards decreases alongside acceleration, until the resultant force is zero and the object falls at a constant speed.
50
What is terminal velocity?
When the resultant force of a falling object is zero and the object is falling at a constant speed.
51
How can forces change shape or size?
The object can stretch,compress, bend or twist
52
Why do you need two forces to change the shape or size of an object?
Because otherwise the object would simply move in the direction of the applied force
53
What happens if a spring is supported at the top and a weight as attached to the bottom?
It stretches
54
What is the amount a spring stretches known as?
The extension
55
An object goes back to its original shape and length after the force is removed. What is this called?
Elastic deformation
56
What happens to An inelastically deformed object after the force is removed
It does not return to its original shape
57
What is the first part of an extension load graph?
A straight line through the origin. Extension and load are in direct proportion.
58
What is the point called when an object becomes inelastically deformed and the graph curves?
The limit of proportionality
59
What does Hooke’s law describe?
How extension varies with force
60
Hooks Law formula
F = kx
61
Describe an experiment to investigate the link between force and extension
1. Measure the natural length of a spring, clamped to a stand, with a millimetre ruler. Make sure you measure it at eye-level.
2. Add a 100g mass to the spring and allow it to come to rest. Record the new length the extension is the change in length.
3. Repeat this process until you have enough measurements.
4. Plot your results on a load against extension graph.
62
What happens when a force acts around a fixed point called a pivot?
A turning effect called a moment is produced
63
Moment definition
The moment of a force is a measure of its turning effect
64
Moment word equation
Moment 🟰 force ✖️ perpendicular distance from the pivot
65
Moment letter formula
M 🟰Fd
66
Moment unit
Nm
67
Why are larger spanners more helpful?
The perpendicular distance is greater therefore less force is required to produce the same moment.
68
How do you get the maximum moment?
By pushing at a right angle to the spanner
69
What is the principle of moments?
When an object is balanced:
the total anticlockwise moment 🟰 the total clockwise moment
70
What happens if the moments are not equal
There will be a resultant moment and the object will turn
71
What two things are required for an object to be in equilibrium?
No resultant force and no resultant moment
72
Describe an experiment to find the moment on a beam in equilibrium
1. Rest a beam on a pivot until it balances.
2. Whilst supporting the beam, Hang a 100g mass on the left hand side at a fixed, 20xm distance.
3. Hand a second mass on the right hand side, move it along until it is balanced.
4. Measure the distance between the pivot on the right hand mass.
5. Calculate the moments using M = Fd
6. Remove the right hand mass, repeat 3-6 using a different mass each time.
73
What is the centre of mass?
The point through which the weight of the object acts. It hangs below the point of suspension.
74
What happens to a freely suspended object?
It swings until the centre of mass is vertically below the point of suspension
75
Why does an object’s centre of mass hang below the point of suspension
Because the weight acts at a perpendicular distance from the pivot, so when vertically below there is no overall moment and the pivot is parallel to the direction of force
76
Describe an experiment to find the centre of mass of a flat shape
1, suspend the shape and a plumb line from the same point and wait until they stop moving
2. Draw a line along the plumb line
3. Do the same thing again, but suspend the shape from a different pivot point
4. The centre of mass is where the lines cross.
77
What does the stability of an object depend on?
Where the centre of mass is
78
If an object is more stable, what properties does it have?
a lower centre of mass and wider base area
79
Why does a more stable object have its properties
If you tilt an object, the centre of mass is no longer directly over where the object is in contact with the ground (pivot). This results in a moment. With a wide base and low centre of mass, the moment will probably cause it to fall back onto the base. However, with a high centre of mass and base, the object will topple more likely.
80
Momentum word formula
Momentum 🟰 mass ✖️ velocity
81
Moment equation letters
p = mv
82
Momentum unit
kg m/s
83
What does the principle of conservation of momentum state?
That the total momentum before 🟰 the total momentum after an event
84
What is an inelastic collision?
When a collision happens, the two objects move off together as one. Do not involve kinetic energy.
85
What is an elastic collision?
When two objects collide they bounce off each other. Use kinetic energy
86
If a momentum before an event is zero, what is the momentum after?
Zero
87
What is an impulse?
The change in momentum
88
Impulse word formula
Impulse = force x time = change in momentum
89
Impulse word formula
Ft = mv - mu
90
Impulse unit
Ns
