Separate Physics - P5 Forces Flashcards
1
Q
What two things does a force arrow show?
A
- The length of the arrow shows the size of the force.
- The direction of the arrow shows the direction of the force.
2
Q
Give some examples of non-contact forces
A
- Gravitational force
- Electrostatic force
- Magnetic force
3
Q
What is a ‘resultant force’?
A
The sum of all forces acting on an object
(the overall force acting on an object)
4
Q
What equation links force, spring constant and extension?
A
Force = spring constant x extension
F = k e
5
Q
Give some examples of contact forces
A
- Friction
- Air resistance
- Tension
- Normal contact force
6
Q
What are the units for:
a) gravitational field strength
b) weight
c) mass
A
a) N/kg
b) N
c) kg
7
Q
What is the equation that links work done, force and distance?
A
Work done = force x distance
W = F s
8
Q
What equation links weight, mass and gravitational field strength?
A
Weight = mass x gravitational field strength
W = m g
9
Q
Why type of energy is stored in a spring that is stretched or compressed?
A
Elastic potential energy
10
Q
What happens to the temperature of an object experiencing friction?
A
Temperature increases
11
Q
What is the name of an object that:
a) will return to its original shape after being deformed
b) will not return to its original shape after being deformed
A
a) elastic
b) inelastic
12
Q
What is the relationship between force and extension of an elastic object?
A
Directly proportional
13
Q
What happens to air resistance as speed increases?
A
As speed increases, air resistance increases.
14
Q
What are typical speed values for someone walking, running and cycling (m/s)?
A
- Walking 1.5 m/s
- Running 3 m/s
- Cycling 6 m/s
15
Q
What is the speed of sound?
A
340 m/s
16
Q
How many forces need to to be applied to this spring to stretch or compress it?
A
Two forces (e.g. one at either end)
17
Q
What equation links acceleration, final velocity, initial velocity and time?
A
18
Q
What equation links distance travelled, speed and time?
A
Distance travelled = speed x time
s = v t
19
Q
Why does a falling object reach terminal velocity?
A
- The resultant force on the object is zero.
- Forces of weight and air resistance are balanced.
20
Q
Name the point on the graph labelled ‘X’
A
Limit of proportionality
21
Q
Describe the motion in the following distance-time graph at points a, b, c and d.
A
a) constant speed
b) stationary
c) accelerating
d) decelerating
22
Q
If you wanted to investigate how mass affects acceleration, what part of the equipment would you change?
A
The mass of the trolley (by adding more masses to the trolley).
23
Q
Which part of the equipment measures acceleration?
A
Light gate
24
Q
If you wanted to investigate how force affects acceleration, what part of the equipment would you change?
A
The force pulling the trolley (by adding more masses to the hook).
25
What is the equation for Newton’s Second Law that links force, mass and acceleration?
Force = mass x acceleration
F = m a
26
Give three factors that can affect braking distance.
* Road conditions
* Weather conditions: wet / icy roads
* Vehicle conditions: condition of brakes / tyre tread depth
27
What equation links momentum, mass and velocity?
Momentum = mass x velocity
p = m v
28
What happens if a car undergoes a large deceleration?
Brakes overheating / loss of control
29
Describe the motion of a moving car experiencing **_balanced_** forces.
Keep moving at a constant speed
30
Describe the motion of a moving car experiencing **_unbalanced_** forces.
The car will change speed (either accelerate or decelerate)
31
Describe the motion of a stationary car experiencing **_balanced_** forces.
The car will remain stationary.
32
Describe the motion of a stationary car experiencing **_unbalanced_** forces.
The car will accelerate.
33
What are typical everyday speeds for cars, trains and planes?
* Car 25 m/s
* Train 55 m/s
* Plane 250 m/s
34
What is stopping distance?
The sum of the thinking distance and the braking distance
35
What is braking distance?
The distance covered during the braking force.
36
What are ‘typical’ reaction times?
0.2 s to 0.9 s
37
What is Newton’s Third Law?
Whenever two objects interact, the forces they exert on each other are **equal in size** and **opposite in direction**.
38
What is thinking distance?
The distance covered during the driver’s reaction time.
39
How does speed affect stopping distance?
Stopping distance increases with speed.
40
Give three factors that can affect a driver’s reaction time.
* Tiredness
* Drugs
* Alcohol
41
What is work done the same as?
Energy transferred
42
If your mass on Earth is 50 kg, what would be your mass on the moon?
The same, 50 kg.
Your mass does not change.
43
What are the units for:
a) force
b) acceleration
c) weight
d) mass
a) N
b) m/s2
c) N (weight is a force)
d) kg
44
Name the forces acting on the book.
45
Calculate the resultant force on the box
0 N (there is no resultant force)
46
Calculate the resultant force on the box.
2N to the left
47
Describe the experiment to investigate how force affects the extension of the spring.
* Measure the starting length of the spring using the ruler.
* Add one 10 g mass, measure the extension of the spring using the ruler.
* Repeat 5 times, each time adding one 10 g mass and measuring the extension of the spring.
48
**Higher Q.** What is inertia?
The tendency of objects to continue in their state of rest / uniform motion
49
**Higher Q.** How can the displacement of an object (the distance travelled) be calculated from a velocity-time graph?
The area under a velocity-time graph
50
**Higher Q.** What is inertial mass?
A measure of how difficult it is to change the velocity of an object.
51
**Higher Q.** How can the motion of an object in a circle be described?
Constant speed but changing velocity
52
**Separate Q**. What equation links force, distance and moment of a force?
Moment of a force = force x distance
53
**Separate Q.** What is a moment?
A turning effect of a force
54
**Separate Q.** What are the SI units for:
a) moment
b) force
c) distance
a) newton-metres, Nm
b) newtons, N
c) metres, m
55
**Separate Q**. In order to calculate the moment of a force, how should distance be calculated in relation to the pivot?
Distance should be calculated perpendicular to the pivot.
56
**Separate Q.** If the first gear is turned clockwise, what direction will the other gears turn in?
\*arrows show the direction (clockwise or anticlockwise)
57
**Separate Q.** Explain how a lever makes it easier for us to do ‘work’.
* Levers increase the distance between the pivot and the force applied.
* You then need to apply less force to achieve the same moment because: **moment = force x distance**
58
**Separate Q.** Pressure in a liquid causes a force to be applied to the surfaces of its container. At what angle is the force applied to the surface of the container?
Right angles / 90o
59
**Separate Q.** Explain how different sized gears can be used to change the size of a moment.
* A force transmitted from a smaller gear to a larger one will cause a bigger moment (and vice versa).
* This is because the distance to the pivot is larger because **moment = force x distance.**
60
**Separate Q.** Explain the relationship between speed and stopping distance in this graph.
* Stopping distance is the sum of the thinking distance and braking distance.
* Thinking distance increases linearly with speed.
* As speed doubles, braking distance increases 4-fold.
* Because of this, braking distance (and hence the stopping distance) increases at a greater rate as speed increases.
61
**Separate Q.** Explain how gears can transmit moments.
* Gears have teeth which interlock with other gears.
* Rotating one gear will cause the adjacent gear to rotate in the opposite direction.
* They can transmit the moment of a force from one place to another.
62
**Separate Q.** If an object is balanced, what is true about the size of the clockwise and anti-clockwise moments?
They are equal in size.
63
**Separate Q.** What two states of matter can be described as a fluid?
A liquid or a gas
64
**Separate Higher Q.** Describe and explain the relationship between the density of a liquid and pressure.
* Density is a measure of the mass of particles per unit volume.
* The denser a liquid is, the more particles there are.
* Therefore, with more particles, there are more collisions, so pressure increases as density increases.
65
**Separate Q.** Describe and explain the relationship between atmospheric pressure and height.
* As the height above Earth increases, atmospheric pressure decreases.
* This is because as altitude increases, the atmosphere becomes less dense.
* This means there are fewer particles, resulting in fewer collisions with the Earth’s surface.
* Also, as altitude increases, there are fewer air particles above, therefore there is a decrease in the weight of particles from above causing a decrease in pressure.
66
**Separate Higher Q.** If an object floats, what is the relationship between its weight and upthrust?
Weight equals upthrust.
67
**Separate Higher Q.** What happens to an object if it is denser than the fluid it is placed in?
It will sink – it weighs more than the equivalent volume of fluid it has displaced
68
**Separate Q.** What equation links pressure, force and area?
69
**Separate Higher Q.** What two things does pressure in a liquid depend on?
* Depth
* Density of the liquid
70
**Separate Higher Q.** Explain why an object in a fluid experiences upthrust.
* Pressure increases with depth.
* Therefore pressure is greatest at the bottom of the object compared with the top.
* This creates a resultant force upwards (upthrust).
71
**Separate Higher Q.** What happens to an object if it is less dense than the fluid it is placed in?
It will float – it weighs less than the equivalent volume of fluid it has displaced
72
**Separate Q.** What is the atmosphere around Earth and how does it change with altitude?
A thin layer of air around the Earth which gets less dense with increasing altitude
73
**Separate Q.** Explain why braking distance increases by 4-fold as speed doubles.
When a car stops, its kinetic energy store decreases to 0 J.
Ek = 1/2mv2 means that as the speed of a car doubles, it’s kinetic energy increases 4-fold.
Work done = energy transferred.
So the work done to stop the car increases by 4-fold.
W = Fs means that under a constant braking force, the braking distance will also increase 4-fold.
74
**Separate Q.** What happens to momentum when a force acts on an object that is moving or able to move?
A change in momentum occurs
75
**Separate Higher Q.** What’s the relationship between upthrust acting on an object and the weight of the fluid displaced by the object?
Upthrust is equal to the weight of the fluid displaced by the water.
76
**Separate Q.** What causes atmospheric pressure?
Air molecules colliding with a surface
77
**Separate Q.** Give examples of safety features used to reduce the rate of change of momentum.
* Air bags
* Seat belts
* Gymnasium crash mats
* Car crumple zones
* Cycle helmets
* Cushioned surfaces on playgrounds
78
**Separate Q.** What are the SI units for:
a) Pressure
b) Force
c) Area
a) Pressure is measured in pascals (Pa)
b) Force is measured in newtons (N)
c) Area is measured in metres squared (m2)
79
**Separate Higher Q.** Describe and explain the relationship between the depth of a liquid and pressure.
* As depth increases, pressure increases.
* Because, as depth increases, the number of particles above increases.
* Pressure increases because of the increased weight of particles above.
80
**Separate Q.** Calculate the velocity of a 2 g bullet that is fired from a 1 kg gun. The gun has a recoil of -0.2 m/s.
\*This is just an example, this type of calculation can be applied to any explosion event.
Momentum before = 0 kgm/s (because the gun and bullet are stationary).
Momentum of gun after (p = mv):
= 1 kg x -0.2m/s = -0.2 kgm/s
Momentum before = momentum after
Momentum of bullet must be +0.2 kgm/s to make the momentum after = 0 kgm/s (same as before).
v= p/m therefore velocity of bullet = +0.2 kgm/s ➗ 0.002 kg = 100 m/s
81
**Separate Q.** Explain how safety features (e.g. seat belts, air bags e.t.c) work to reduce injuries to a person.
* They increase the time taken to stop.
* This decreases the rate of change of momentum.
* This reduces the force on the person because:
* F = (m𝝙V)/𝝙t
* Therefore reducing the injuries to the person.
82
**Separate Q.** A 50 kg skater is skating from left to right at a velocity of 2 m/s. A 75 kg skater is skating from right to left with a velocity of 1.5 m/s. The two skaters collide and skate away together. Calculate the velocity of the skaters as they move away.
\*This is just an example, this type of calculation can be applied to any collision event.
\*This answer assumes left to right as positive.
Skater 1 momentum: 50 kg x 2 m/s = +100 kgm/s
Skater 2 momentum: 75 kg x 1.5 m/s = -112.5 kgm/s
Momentum before = +100 + -112.5 = -12.5 kg m/s
momentum before = momentum after
Momentum after = -12.5 kg m/s
Combined mass of skaters = 50 + 75 = 125 kg
v= p/m therefore velocity of skaters = -12.5 kgm/s ➗ 125 kg = -0.1 m/s
