Chapter 4 Forces in Action

Question 1

What is the equation for force?

Answer 1

Force = Mass x Acceleration

Question 2

What is the equation to find weight?

Answer 2

Weight = Mass x Force of gravity

Question 3

What is weight?

Answer 3

It is the amount of Newtons of force that the earth is attracting the object

Question 4

What is the centre of mass?

Answer 4

This is the position at which all the mass of an object appears to be

Question 5

What is the centre of gravity?

Answer 5

This is the position at which all the weight of the objecct appears to be

Question 6

What is the method / experiment to find the centre of gravity?

Answer 6

1. Hang the object from a point that is off centre
2. Draw a line vertically down from the point. Use a guide to help you know where to draw the line (e.g. a weight on a string).
3. Repeat steps 1 and 2 until all the points cross at one point. This point is the centre of gravity

Question 7

Name some important forces that can act on an object

Answer 7

Weight
Friction
Drag
Tension
Upthrust
Normal contact force

Question 8

What is a free-body diagram?

Answer 8

It is a diagram that isolates and shows all the forces acting on an object

Question 9

What are the two factors that affect the drag force of an object?

Answer 9

The speed and the cross-sectional area

Question 10

What is terminal velocity?

Answer 10

This is when the force of the weight moving the object through a fluid is equal to the drag force exerted on the object

Question 11

What is a moment?

Answer 11

This is turning force of an object

Question 12

What is the equation of a moment?

Answer 12

Moment = Force x perpendicular distance of the line of action of force from axis or point of rotation

Question 13

What is the principle of moments?

Answer 13

When in equilibrium, the magnitude of the clockwise force is equal to the magnitude of the anticlockwise force

Question 14

What is a couple?

Answer 14

This is the pair of forces acting on an object that rotates around a pivot point. The two forces must be parallel and along different lines.

Question 15

What is the equation for a couple?

Answer 15

Moment = (F1 x d/2) + (F2 x d/2)
or if F1 and F2 are equal
Moment = F x d

Question 16

How can the resultant force be calculated?

Answer 16

By drawing the forces tip to tail and using trigonometry to work out the resultant force

Question 17

What is density? What is the equation?

Answer 17

It is the mass per unit volume.

ρ = m / v

Question 18

How can the exact volume of an object be easily calculated?

Answer 18

Place the object in water and work out the change in the level of the water. Use this to work out the volume which is equal to the volume of the object.

Question 19

What is the equation of pressure?

Answer 19

Pressure = Force / Cross-sectional area

Question 20

What are fluids?

Answer 20

Gasses and liquids

Question 21

What is the equation to work out the pressure exerted by a vertical column of liquid?

Answer 21

p = hρg
h = height of water above object
ρ = density of the liquid
g = force of gravity

Question 22

What is upthrust?

Answer 22

This is the force pushing an object up through a liquid

Question 23

What is the equation for upthrust?

Answer 23

Upthrust = Axρg
A = Cross sectional area of the object placed in the fluid
x = The depth of the object placed in the fluid
So ax is the volume of the object placed in the fluid
ρ = the density of the fluid
g = The force of gravity on the fluid the object is submerged in

Question 24

What is archimedes principle?

Answer 24

The upthrust on an object is equal to the weight of the volume of fluid that it displaces