Forces and Motion Flashcards
(82 cards)
1
Q
Straight line on a distance time graph
A
Constant speed
2
Q
Flat (horizontal) line on a distance time graph
A
Object is not moving
3
Q
Steep gradient on a distance time graph
A
Faster speed
4
Q
Shallow gradient on a distance time graph
A
Slower speed
5
Q
What is speed?
A
The distance travelled over a given time
average speed = distance / time
- average speed (m/s)
- distance (m)
- time (s)
6
Q
How do you find the average speed on a distance time graph?
A
Average speed = gradient of a distance-time graph
1. Find the start distance (d1) and start time (t1)
2. Find the final distance (d2) and final time (t2)
3. v = change in distance / change in time = d2 - d1 / t2 - t1
7
Q
PRACTICAL: investigate the motion of everyday objects such as toy cars or tennis balls
A
- Measure the distances using a measuring stick (metre stick/trundle wheel)
- Measure time using a stopwatch
- Calculate speed using speed= distance/time
8
Q
Acceleration equation
A
Acceleration = Change in velocity / Time
- acceleration (m/s^2)
- change in velocity (m/s)
- time (s)
a = v - u / t
- v = final velocity
- u = start velocity
9
Q
A negative acceleration
A
= Slowing down = deceleration
10
Q
Explain velocity-time graphs
A
A velocity-time graph shows how the velocity (or speed) of a object changes over time
- Velocity is a vector so the line can go up & down
- ‘At rest’ means not moving
- Straight horizontal line at 0 velocity = At rest
- Straight diagonal line (up) = Constant acceleration
- Straight horizontal line = Constant velocity
- Straight diagonal line (down) = Constant deceleration
11
Q
How do you find acceleration on a velocity-time graph?
A
Acceleration= gradient of a velocity-time graph
a = v - u / t = 10 - 0 / 5 - 0 = 2m/s^2
12
Q
How do you find the distance travelled on a velocity−time graph?
A
Distance= area under velocity-time graph
- rectangle: velocity x time
- triangle: 1/2 x velocity x time
13
Q
How to calculate final velocity
A
(final velocity)^2 = (inital velocity)^2 + 2 x acceleration x distance
v^2 = u^2 + 2as
v = final velocity (m/s)
u = start velocity (m/s)
acceleration (m/s^2)
distance (m)
14
Q
When an object (body) experiences a force, one of the following happens:
A
- Change speed
- Change space
- Change direction
15
Q
Contact force
A
If the objects need touch to experience force
16
Q
Non-contact force
A
If the objects do not touch eachother to experience force
17
Q
Examples of contact forces:
A
- Friction
- Air resistance
- Push
- Pull
- Thrust
- Etc.
17
Q
Examples of non contact forces:
A
- Gravitational
- Electrostatic
- Magnetic
18
Q
Gravitational force
A
Attractive only
Affects objects with mass
Non-contact
19
Q
Electrostatic force
A
Attractive or repulsive
Affects objects with charge
Non-contact
20
Q
Magnetic force
A
Attractive or repulsive
Affects objects with poles or magnetic materials
Non-contact
21
Q
Normal reaction force
A
- The force between 2 objects in constant contact
- Works at 90*c to the contact between 2 objects
22
Q
What is the difference between a vector & scalar quantity?
A
Scalar: only has magnitude (size), it doesn’t have a direction e.g. distance, speed
Vector: has magnitude (size) and direction e.g. displacement (distance with direction), velocity (speed with direction)
23
Q
Examples of scalar quantities:
A
Speed (e.g., 30 m/s)
Distance (e.g., 100 m)
Time (e.g., 5 seconds)
Mass (e.g., 50 kg)
Energy (e.g., 200 J)
Temperature (e.g., 25°C)
24
Examples of vector quantities:
Velocity (e.g., 20 m/s east)
Displacement (e.g., 5 m north)
Acceleration (e.g., 3 m/s² downward)
Force (e.g., 10 N to the right)
Momentum (e.g., 15 kg·m/s forward)
25
What is resultant force?
The overall force acting on an object
26
How do you calculate the resultant force of forces that act along a line?
- Resultant force is the overall force acting on an object:
- Opposite forces: Big number take away small number
- Same direction forces: Added together
27
What is friction?
- The force that opposes the motion of an object
- Occurs when 2 or more objects are rubbing against eachother
28
What is Newton’s First Law?
- If forces are equal & opposite ,forces are balanced/in equilibrium, an object stays still or at a constant velocity
- If forces are not equal & opposite, forces are unbalanced velocity changes (an object speeds up, slows down, or changes direction)
29
What is Newton’s Second Law?
- As resultant force increases, acceleration increases
- As mass increases, acceleration decreases
30
What is the gravitational field strength on earth?
10m/s²
31
Equation for weight:
weight (N)= mass (kg) x gravitational field strength (m/s²)
32
Stopping distance=
Stopping distance= Thinking distance + Braking distance
33
What is stopping distance?
The total distance required for a car to stop moving
34
What is thinking distance?
The distance it takes for a driver to react & press the brake pedal
35
What is braking distance?
The distance it takes between when the brake pedal is pressed & the car halts
36
Factors affecting stopping distance of a vehicle:
- Physical factors that affect the amount of friction between the brake pads and the wheel, or the tyre and the road, will affect the braking distance
- Factors that affect the thinking/reaction time of the driver will affect the thinking distance
37
What factors affect thinking distance?
- Driver’s reaction time
- Intoxication (consumption of drugs or alcohol)
- Distraction to the driver
- Tiredness
38
What factors affect braking distance?
- Mass of vehicle
- State of vehicle’s brakes
- State of road
- Friction between tyre & road
39
What factors affect braking & thinking distance?
Speed of vehicle
40
Describe the forces acting on falling objects
When objects fall:
1. Weight accelerates object
2. Weight is greater than air resistance
3. As velocity increases, air resistance increases & acceleration decreases
4. Eventually weight = air resistance
5. The object reaches a maximum speed called terminal velocity
41
Elastic distortion
When 2 or more forces act on the same object, the object can be stretched, compressed or bent.
- A change of shape is called distortion
- Elastic distortion = temporary
- Inelastic distortion = permanent
42
Why is the hot metal being inelastically distorted
Since it will not go back to its original shape
43
Why is the pole being elastically distorted
Since it will go back to it's original shape
44
What happens when a force is applied to an elastic object?
The object stretches in a linear fashion, following a straight-line relationship between force and extension. This means it obeys Hooke’s Law.
- Extension v Force graph
1. 1st part of graph obeys Hooke's Law
-> A linear relationship is observed
Limit of proportionality -> when line changes direction
2. 2nd part of graph doesn't obey Hooke's Law
-> The object has become permanently stretched
45
What happens when an elastic object is stretched beyond the limit of proportionality?
The object stops obeying Hooke’s Law, becomes permanently stretched, and the force-extension relationship becomes non-linear.
46
How do you calculate extension?
Extension = New length - Original length
47
What does Hooke’s Law state?
Force is directly proportional to extension, up to a limit of proportionality.
48
PRACTICAL: investigate how extension varies with applied force for helical springs, metal wires and rubber bands
1. Set up a clamp stand with a ruler & attach the material (spring, wire, or rubber band).
2. Measure the initial length of the material without any load.
3. Attach a weight hanger and gradually add weights, recording the new length after each addition.
4. Calculate extension using:
Extension = New Length - Original Length
5. Repeat for each material and plot a force vs. extension graph.
49
Observations – Helical Spring
- Follows Hooke’s Law: Extension is proportional to force (F = kx).
- Returns to its original length if force is removed before the elastic limit.
- Beyond the elastic limit, it deforms permanently & no longer obeys Hooke’s Law.
50
Observations – Metal Wire
- Initially obeys Hooke’s Law, showing proportional extension.
- After exceeding the elastic limit, it stretches permanently & does not return to its original shape.
- Behaves like a spring at first but can suffer plastic deformation
51
Observations – Rubber Band
- Does not follow Hooke’s Law – extension is not proportional to force.
- Stretches easily at first, but harder to stretch more.
- Takes time to return to its original shape after force is removed (lag in recovery).
52
PAPER 2 Momentum equation:
Momentum (kgm/s) = Mass (kg) x Velocity (m/s)
p = m x v
Momentum is a vector quantity -> has both magnitude (size) and a direction
53
PAPER 2 What is the Law of Conservation of momentum?
Says that:
The total momentum of a system before a collision = The total momentum of a system after the collision
P before = P after
54
PAPER 2 How to answer a momentum question:
1. Draw the situation
2. Calculate the total momentum before the collision
3. Calculate the total momentum after the collision
4. Use the conservation of momentum to solve
55
State the equation linking force, mass an acceleration
F = m x a
Force = Mass x Acceleration
56
PAPER 2 State the equation linking force, mass, change in velocity, and time
F = m x (v-u/t)
Force = mass x change in velocity over time
57
PAPER 2 State the equation linking force, change in momentum and time
F = mv-mu/t = ∆p/t
Force = change in momentum divided by time
58
PAPER 2 If you increase t, you can reduce the……….
impact force from large deceleration
59
PAPER 2 Crumple zones
- Crumple on impact, increasing the time taken for the car to stop
- Because F = ∆p/t, the greater the time of the collision, the lower the force applied, the lower chance of injury or death
60
PAPER 2 Seat belts
- Stretch slightly, increasing the time taken for the wearer to stop
- Reduces the forces acting on the chest
- Because F = ∆p/t, the greater the time of the collision, the lower the force applied, the lower chance of injury or death
61
PAPER 2 Air bags
- Slow you down (decelerate) more gradually
- Because F = ∆p/t, the greater the time of the collision, the lower the force applied, the lower chance of injury or death
62
PAPER 2 State Newton’s Third Law
Every force applied has a reaction force that is:
- equal in magnitude (size)
- opposite in direction
- Acting on a different object
- “For every force there is an equal & opposite reaction
63
PAPER 2 N3L: To work out the other force in an action reaction pair….
Swap the objects around
We are attracted to the Earth by weight
The Earth is attracted to us by weight
64
Thrust and friction
Balanced forces are equal & opposite, but act on the same object
65
PAPER 2 Car pushes on road, road pushes on car
Action-reaction pairs (aka force pairs) are equal & opposite, but act on different objects
66
PAPER 2 If a force is applied at right angles to an object that is attached to a pivot, the object will…
the object will rotate
67
PAPER 2 The greater the distance from the pivot, the easier the ….
the easier this rotation will be
68
PAPER 2 State the equation linking moment, force and perpendicular distance from the pivot
Moment of a force (Nm) = Force (N) x distance normal to the direction of the force/perpendicular distance (m)
M = F x d
69
PAPER 2 State the principle of moments
The sum of clockwise moments = The sum of anti-clockwise moments
70
PAPER 2 To solve moments in equilibrium:
1. Calculate the sum of clockwise moments
2. Calculate the sum of anti-clockwise moments
3. Clockwise moments = Anti-clockwise moments
4. Solve for the missing value
71
PAPER 2 Centre of Gravity
(centre of mass) the point through which the weight of the object acts
If an object is suspended, it will swing until the centre of gravity is directly below the point of suspension.
72
PAPER 2 Line of action
Weight acts straight down from the centre of mass
An object will topple if its line of action is outside its base
73
PAPER 2 Where is the center of mass located in a symmetrical 2D object?
The center of mass is along the line of symmetry.
If there are multiple lines of symmetry, it is where they intersect.
74
PAPER 2 How can a light beam be treated in physics problems?
A light beam can be treated as if it has no mass.
75
PAPER 2 What happens when a light beam is supported at both ends?
It supplies an upward force to any weighted object placed on the beam.
76
PAPER 2 If a weighted object is placed on a supported beam, which support provides more upward force?
The support closer to the object provides more upward force.
77
PAPER 2 How do you find the upward forces on a light beam?
Choose one support as the pivot.
Use the principle of moments to find one force.
Use the equation F(A) + F(B) = F(down) to find the other force.
78
Straight horizontal line at 0 velocity on a velocity time graph
At rest
79
Straight diagonal line (up) on a velocity time graph
Constant acceleration
80
Straight horizontal line on a velocity time graph (not at 0)
Constant velocity
81
Straight diagonal line (down)
Constant deceleration
