Forces

Question 1

Give 2 names for the instrument you can use measure the weight of an object.

Answer 1

Netwonmeter (callibrated spring balance)

Question 2

1 joule = ?

Answer 2

1 newton-metre

Question 3

What must there be in order to change the shape of a stationary object?

Answer 3

At least 2 forces e.g. pushing the sides of a bottle to squash it.

Question 4

Elastic limit.

Answer 4

The furthest point a material can be deformed where it can return to its original shape when the force is removed.

Question 5

Load.

Answer 5

The force exerted on a surface or body (e.g. the load is the weight force downwards for a wheelbarrow in action).

Question 6

What is d in M=Fd?

Answer 6

The perpendicular distance from the pivot to the line of action of the force.

Question 7

Define a force multiplier and give two examples.

Answer 7

A tool that increases the distance between an object and a perpendicular force, decreasing the force needed to rotate it e.g. spanners, pulleys, crowbars.

Question 8

Explain how gears work.

Answer 8

A series of gears transmit the rotational effect of a force from one place to another. They can be different sizes to change the moment of a force.

Question 9

Smaller gears rotate ____er.

Answer 9

faster

Question 10

Do bigger gears have a bigger or smaller moment? Explain why.

Answer 10

The bigger the gear, the bigger the moment, as the distance from the centre of the gear to the edge is larger (and M=Fd).

Question 11

What does the turning effect of a gear mean?

Answer 11

The rotational force.

Question 12

Gear B has twice the radius of gear A. Gear A rotates, causing gear B to rotate. How does the work each gear does compare?

Answer 12

The same amount of work is done by the two gears as gear A rotates twice as much as gear B.

Question 13

Explain why an object suspended in a fluid may float.

Answer 13

• A submerged object experiences a greater force on its bottom than its top.
• The pressure difference creates an upwards resultant force (upthrust).
• The object is less dense than the fluid, so has a smaller weight than the equivalent volume of water.
• This means it displaces a volume of fluid that is equal to its weight.
• The upthrust is equal to the weight of the displaced fluid.
• This means the downwards weight force is equal to the upwards upthrust, so the object floats.

Question 14

Explain why an object suspended in a fluid may sink.

Answer 14

• A submerged object experiences a greater force on its bottom than its top.
• The pressure difference creates an upwards resultant force (upthrust).
• The object is more dense than the fluid, so has a bigger weight than the equivalent volume of water.
• This means it cannot displace a volume of fluid that is equal to its weight.
• The upthrust is equal to the weight of the displaced fluid.
• This means the downwards weight force is greater than the upwards upthrust, so the object sinks.

Question 15

What is the difference between inertia and inertial mass?

Answer 15

Inertia = the tendency of an object to continue in its current state of motion
Inertial mass = the measure of how difficult it is to change an object’s state of motion (its velocity)

Question 16

What are the typical reaction times of a person?

Answer 16

0.2-0.9s

Question 17

If the velocity of a car doubles, the stopping distance ____.

Answer 17

increases by a factor of 4

Question 18

Why is a large deceleration of a vehicle dangerous? Give two reasons.

Answer 18

• The brakes can overheat.
• The driver can lsoe control of the vehicle.