1 Forces and Motion

Question 1

distance time graphs

Answer 1

A constant gradient represents constant speed

The gradient of the line represents the speed:
A very steep gradient means the object is moving at a large speed
A shallow gradient means the object is moving at a small speed
A flat, horizontal line means the object is stationary (not moving)

Objects might be accelerating - this is represented by a curve
In this case, the gradient of the line will be changing
If the gradient is getting steeper, the speed is increasing (accelerating)
If the gradient is getting shallower, the speed is decreasing (decelerating)

The speed of a moving object can be calculated from the gradient of the line on a distance-time graph

Question 2

speed, distance and time equation

Answer 2

speed = distance / time

Question 3

practical: investigate the motion of everyday objects such as toy cars or tennis balls

Answer 3

Measure out a height of 1.0 m using the tape measure or metre ruler
Drop the object from this height, which is the distance travelled by the object
Use the stop clock to measure how long the object takes to travel this distance
Record the distance travelled and time taken
Repeat steps 2-3 three times, calculating an average time taken for the object to fall a certain distance
Repeat steps 1-4 for heights of 1.2 m, 1.4 m, 1.6 m, and 1.8 m

Question 4

acceleration, time taken and change in velocity equation

Answer 4

acceleration = change in velocity / time taken

Question 5

velocity time graphs

Answer 5

The gradient of the line represents the magnitude of acceleration
A steep gradient means large acceleration
A shallow gradient means small acceleration
A positive gradient (upward slope) shows increasing velocity -> acceleration
A negative gradient (downwards slope) shows decreasing velocity -> deceleration
A horizontal line means the acceleration is zero so the object is moving with a constant velocity

Question 6

how to find acceleration from a velocity time graph

Answer 6

calculated from gradient of the line

Question 7

how to find the distance traveled on a velocity time graph

Answer 7

find the area under the line

Question 8

what does kg measure

Answer 8

mass

Question 9

what does N/kg measure

Answer 9

gravitational field strength or acceleration due to gravity

Question 10

what are the effects of forces between bodies

Answer 10

When a force acts on an object, the force can affect the object in a variety of ways
The object could:
change speed
change direction
change shape

Question 11

types of forces

Answer 11

Gravitational (or weight) - the force between any two objects with mass (like the Earth and the Moon)
Electrostatic - the force between any two objects with charge (like a proton and an electron)
Thrust - the force pushing a vehicle (like the push from rocket engines on the shuttle)
Upthrust - the upward force on any object in a fluid (like a boat on the surface of a river)
Air resistance (or drag) - the force of friction between objects falling through the air (like a skydiver in freefall)
Compression - forces that squeeze an object (like squeezing a spring)
Tension - forces that stretch an object (like two teams in a tug-of-war)
Reaction force - the force between any two objects in contact (like the upwards force from a table on a book)

Question 12

what is the difference between vectors and scalers

Answer 12

Scalars are quantities that have magnitude but not direction
Vectors are quantities that have both magnitude and direction

Question 13

examples of vectors

Answer 13

displacement
force
weight
velocity
acceleration
momentum

Question 14

what is a force that opposes motion

Answer 14

friction

Frictional forces always act in the opposite direction to the object’s motion
Friction occurs when two (or more) surfaces rub against each other
At a molecular level, both surfaces contain imperfections - i.e. they are not perfectly smooth
These imperfections push against each other

Question 15

examples of scalers

Answer 15

distance
speed
mass
energy
temperature

Question 16

force, acceleration and mass equation

Answer 16

force = mass x acceleration

Question 17

weight, mass and gravitational field strength equation

Answer 17

weight = mass x gravitational field strength

Question 18

what is the stopping distance

Answer 18

thinking distance + braking distance

Question 19

what factors affect the vehicles stopping distance

Answer 19

speed
mass of car
condition of cars breaks
road condition
reaction time

Question 20

forces acting on falling objects

Answer 20

Weight
Air resistance

The force of air resistance increases as the object’s speed increases
This is because the object collides with air particles as it moves through the air
The faster the object is travelling, the more collisions it has with the air particles

Question 21

terminal velocity

Answer 21

Terminal velocity is the fastest speed that an object can reach when falling
Terminal velocity is reached when the upward and downward acting forces are balanced
The resultant force on the object reaches zero
The object no longer accelerates and a constant terminal velocity is reached

Question 22

skydiver example of terminal velocity

Answer 22

At the instant the skydiver steps out of the plane, the support force of the plane is no longer acting on the skydiver, but they are not yet falling, so the only force exerted them is the weight force
There is a downward acting resultant force on the skydiver
The resultant force is equal to the weight force
The skydiver accelerates downward at maximum acceleration

As the skydiver begins to fall, the force of air resistance is very small because the skydiver’s speed is small
There is a downward acting resultant force on the skydiver
The resultant force is equal to the weight force minus the force of air resistance
The skydiver accelerates downward but the acceleration decreases

As the skydiver accelerates, their speed increases, so the force of air resistance increases
There is a downward acting resultant force on the skydiver
The resultant force is equal to the weight force minus the force of air resistance
The skydiver accelerates downward but the acceleration continues to decrease

As the skydiver’s acceleration decreases, their speed increases at a slower and slower rate
Eventually, the skydiver reaches a speed at which the force of air resistance is equal to the force of weight
The forces are balanced, so the resultant force is zero
The skydiver no longer accelerates and a constant velocity is reached
This is terminal velocity

Question 23

equation with initial speed, final speed, distance moved and acceleration

Answer 23

(final speed)^2 = (initial speed)^2 + (2 x acceleration x distance moved)

Question 24

how to calculate the resultant force that acts along a line

Answer 24

largest force - smallest force