Chapter 8 - Forces in Balance

Question 1

What is displacement?

Answer 1

Distance in a given direction.

Question 2

Define a vector quantity.

Answer 2

A quantity with magnitude and direction.

Question 3

Define a scalar quantity.

Answer 3

A quantity with magnitude but no direction.

Question 4

Define vector.

Answer 4

Physical quantities which have direction.

Question 5

Define magnitude.

Answer 5

The size of a quantity.

Question 6

Define magnitude.

Answer 6

The size of a quantity.

Question 7

State Newton’s third law.

Answer 7

When 2 objects interact, they exert equal and opposite forces on each other.

Question 8

What is a contact force?

Answer 8

A force acting on objects only when they are touching.

Question 9

Give 3 things that forces can do to an object.

Answer 9

Change shape of the object.
Change motion of object.
Change state of rest of object.

Question 10

Define a resultant force of an object.

Answer 10

A single force which has the same effect of all forces acting on the object.

Question 11

State Newton’s 1st Law.

Answer 11

If forces acting on an object are balanced, the resultant force is zero.

Question 12

What occurs when the resultant force of an object is greater than zero?

Answer 12

The speed/direction of the object will change.

Question 13

Describe how a free-body diagram is used to show different forces acting on an object.

How can you calculate the resultant force from a free body diagram?

Answer 13

This diagram uses arrows to represent vectors, with the arrows pointing in the direction of the force.

You subtract the forward force from the backward force, and the upper force from the lower force, then add them together.

Question 14

What is the moment of a force?

Answer 14

The turning effect of the force of an object.

Question 15

State the equation used to calculate moments.

Answer 15

Moments/M (N) = Force/F (N) x Distance from line of action to pivot/d (m)

Question 16

A force of 79.4N is exerted on a claw hammer of length 3.2m. Calculate the moment of the force.

Answer 16

M = F x d
M = 79.4 x 3.2 
M = 254.08N

Question 17

How do you increase the moment of a force?

Answer 17

Increase force/F

Increase distance from line of action to pivot/d

Question 18

What are the use of gears?

Answer 18

To change the moment of a turning effect.

Question 19

Give 2 examples where a force applied from a longer distance from the pivot can be useful in everyday life.

Answer 19

Using a bottle opener to open the cap of a bottle by applying force further away from the pivot.
Using scissors to cut string by applying force further away from the pivot.

Question 20

What is the centre of mass of an object?

Answer 20

The point where the mass is concentrated.

Question 21

Why does a swing come to rest below the top of the swing?

Answer 21

The equilibrium is located directly under the swing. When no force is applied to the swing, it will be stationary at the equilibrium.