Topic 2 - Motion and Forces

Question 1

2.14 - Explain Newton’s first law

Answer 1

The resultant force is calculated by adding forces in the same direction and subtracting forces in the opposite direction.
If the resultant force is 0, forces are balanced.
Unbalanced forces change an objects speed and direction.
Newton’s first law is when a moving object will continue to move at that speed unless an external force acts on it and a stationary object will remain at rest unless an external force acts on it.

Question 2

2.15 - What equation links force, mass and acceleration?

Answer 2

Force = mass * acceleration
F = ma

Question 3

2.16 - What equation links weight, mass and gravitational field?

Answer 3

Weight = mass * gravitational field strength
W = mg

Question 4

2.17 - Describe how weight is measured

Answer 4

Weight is the pull of gravity on a object, it is measured using a force meter in newtons.

Question 5

2.18 - Describe the relationship between weight and gravitational field strength of a body

Answer 5

Gravitational field strength has a value of 10N/kg, meaning each kilogram is pulled down with a force of 10N.
When mass is multiplied by gfs, you get the weight.

Question 6

2.19 - Core Practical - Investigate the relationship between f,m and a in trolleys

Answer 6

Place one end of the ramp higher and let the ramp move on its own.
Set up light gates, pulley and string.
Find trolleys mass and note it.
Put a mass on the end of the string and don’t change it.
Release the trolley and note its speed as it passes the light gate, note its time from one gate to another.
Put a mass on the top of the trolley, increment these masses.
To find the effect of force on acceleration, mass must be kept constant, but the masses on the trolley can be transferred to the string to see its effect on acceleration.

Question 7

2.20/21 - Explain the forces on an object moving in a circular orbit

Answer 7

Objects in circular orbit have a changing velocity although speed is the same.
The resultant force causing this change is centripetal force and it acts towards the centre of the circular movement.

Question 8

2.22 - Explain inertial mass

Answer 8

More bigger an object is more force is needed to change its velocity, this is its inertial mass and is found by force/acceleration.

Question 9

2.23 - Explain Newton’s third law

Answer 9

Forces come as pairs called action-reaction forces, they are always the same size and in opposite directions.
Action-reaction forces happens when objects collide.
They forces are the same size although the effects will depend on their masses.

Question 10

2.24 - What equation that links momentum, mass and velocity?

Answer 10

Momentum = mass * velocity
p = mv

Question 11

2.25 - Describe what happens to momentum in collisions

Answer 11

When moving objects collide the total momentum of both objects are the same before the collision and after, as long as no external forces act. This is the conservation of momentum.
If objects move in opposite directions, momentum of one object is a positive sign and another is a negative sign.

Question 12

2.26 - What is Newton’s second law?

Answer 12

Force = change in momentum / time
F = (mv-mu)/t
This is derived from f = ma and a = v-u/t

Question 13

2.27 - Explain methods of measuring human reaction times

Answer 13

A reaction time is the time between the detection of the stimulus and their response.
The response times can be measured using computers.
Typical reaction time to stimuli is about 0.25 seconds.

Question 14

2.28 - What is the stopping distance?

Answer 14

When a driver sees a danger stimuli, the vehicle travels a certain distance while the driver reacts. This is the thinking distance.
The vehicle travels further while the brakes work to stop the it. This is the braking distance.
The stopping distance is the sum of the braking and thinking distances.

Question 15

2.29 - Explain that the stopping distance is affected by many factors

Answer 15

Car brakes use friction to slow the car down, if the brakes are worn, less friction is created and the vehicle isn’t stopped as effectively.
If the road is wet or is icy, there is less friction and braking distance is increased.
If a vehicle has more mass, more force is needed to decelerate it, so a heavier vehicle would need more friction to stop it.
As speed of a vehicle increases, more friction is needed to stop the car.

Question 16

2.30 - Describe factors affecting a driver’s reaction time

Answer 16

If the person is ill, tired, taken drugs or alchohol and are using their phone, their reaction time increases.

Question 17

2.31 - What are the dangers of large decelerations and how is it reduced?

Answer 17

In car crashes, a vehicle would slow down quickly, this deceleration depends on the size of acceleration and mass of the object.

Modern cars have crumple zones in the front of the car, when a car crashes the crumple zone is crumpled in order to decrease the force on the car and the passengers.
Seat belts hold passengers in their seats and airbags increase the time for a person’s head to stop in a collision.

Question 18

2.32P/33P - How is the braking distance found?

Answer 18

Use KE = 1/2 mv^2 then plug the energy into w.d = fd to find distance.