Forces and Movement

Question 1

What is the equation for Newtons 2nd Law? (force)

Answer 1

Force = Mass*Acceleration or F = m*a

Question 2

What do forces do to objects?

Answer 2

Forces make objects:

• speed up/slow down
• change direction
• start or stop
• change shape

Question 3

What is the relationship (equation) between weight, mass and g?

Answer 3

Weight = mass*g

Question 4

What is the gravitational field strength measured in?

Answer 4

N/kg

Question 5

When would your weight change?

Answer 5

Weight = mass*g and since mass is constant, g would have to change for your weight to change. G is 1.7 on the moon so if you went to the moon your weight would change.

Question 6

What main forces will act on you if you fall through a fluid.

Answer 6

Gravitational force (downwards) and frictional force (upwards), ignoring Archimedean force.

Question 7

How is the size of the resistive force relative to the speed on a falling object?

Answer 7

The size the resistive force is approximately on the speed squared. The resistive force is the drag force.

Question 8

What will initially happen as a skydiver jumps out of a plane?

Answer 8

There will be zero resistive force and she will be accelerating downwards a rate of 10m/s/s.

Question 9

What will happen when a skydiver picks up speed?

Answer 9

The drag force grows, reducing the overall force downwards and thus reducing the acceleration.

Question 10

What will eventually happen to a free falling skydiver?

Answer 10

The resistive force will become equal to the weight making the overall force and acceleration zero so the object will now fall at a constant velocity.

Question 11

What is it called when an object is falling at a constant velocity?

Answer 11

Terminal velocity.

Question 12

What happens when a skydiver at terminal velocity opens their parachute?

Answer 12

The resistive force is larger than the weight of the skydiver so he is decelerating (but still falling downwards) until his speed falls to a point where his weight again balances the drag force. He will reach terminal velocity again.

Question 13

What actually makes a car decelerate when you apply the brakes?

Answer 13

The friction force between the tires and the road. This force should be as large as possible to make the deceleration as big as possible.

Question 14

Why is over-breaking bad and what factors affect it?

Answer 14

Overbreaking makes it more likely the car will skid and when this happens there is less friction between the wheels of the car and the road. Poor tires, water, ice or oil on the road surface will make the maximum braking force you can apply without skidding much lower so your deceleration is lower.

Question 15

What is the overall stopping distance?

Answer 15

A sum of the thinking and breaking distance.

Question 16

What is the thinking distance?

Answer 16

The distance you travel while thinking about putting your foot on the break.

Question 17

What is the breaking distance?

Answer 17

The distance the car travels once the breaks have been applied.

Question 18

How is the thinking distance related to the speed you are driving at?

Answer 18

It is proportional to the speed.

Question 19

How is the breaking distance related to the speed you are driving at?

Answer 19

On the speed SQUARED.

Question 20

How do you calculate breaking distance?

Answer 20

Breaking distance = Average speed*time

Question 21

What factors while affect your reaction time?

Answer 21

Age, eyesight, tiredness, drugs, alcohol, medicines, mobile phones etc.

Question 22

What factors will affect the breaking distance?

Answer 22

• The speed
• The mass of the car
• The braking force

or even anything on the road such as ice that reduces the friction

Question 23

What is the law to do with acceleration due to gravity and weight?

Answer 23

All object accelerate at the same soeed on earth, provided that the effect of air resistance can be ignored. This can be demonstrated by the ‘coin and feather’ eperiment in which the two objects take exactly the same amount of time to fall through a tube with no air in it.

Question 24

Why does a light object (e.g. a feather) fall slower than a heavy object (e.g. a hammer), even though it has a lower force of air resistance?

Answer 24

Because the feather has a lower mass so it reaches terminal velocity (when drag=weight) sooner than the hammer

This is becasue a smaller drag force is needed to the avergae velocity of the feather is lower so it falls slower