Module 3 - Chapter 4 - Forces in action

Question 1

What is the equation for force?

Answer 1

F = ma
Force = mass x acceleration

Question 2

What is the unit for force?

Answer 2

Newtons (N)

Question 3

What is the equation for weight?

Answer 3

w = mg
weight = mass x gravitational field strength

Question 4

What is the unit for weight?

Answer 4

Newton (N)

Question 5

What is the centre of gravity?

Answer 5

The centre of gravity is where all of an objects weight can be assumed to be acting upon

Question 6

What is the difference between the centre of gravity and centre of mass?

Answer 6

They are normally the same but if the gravitaional field the object is in isn’t uniform, then the centre of gravity will be at a different point.

Question 7

How can you find the centre of gravity?

Answer 7

When an object is suspended freely, its centre of gravity will naturally come to rest directly vertically below the point of suspension. Use a plumb line and a pen to mark this line. Then do it again from a different point of suspension and the point where the two lines cross is the centre of gravity.

Question 8

How do you show all the forces acting on an object?

Answer 8

Using a free body diagram

Question 9

Name 5 forces

Answer 9

weight
friction
drag
tension
upthrust
normal contact force

Question 10

State the equations to find the force parallel and perpendicular to a slope

Answer 10

force parallel to the slope = wsinθ
force parallel to the slope = weight x sinθ

force perpendicular to the slope = wcosθ
force perpendicular to the slope = weight x cosθ

Question 11

How would you find the normal contact force?

Answer 11

Using the equation to find the force perpendicular to the slope

Question 12

Explain what happens when an object hits terminal velocity

Answer 12

When an object reaches terminal velocity, the drag force will be equal to the weight force and so there will be no vertical resultant force and the object will not be accelerating or decelerating vertically.

Question 13

What is the moment of a force?

Answer 13

The moment of a force is the turning effect of a force about the same axis or point.

Question 14

What is the equation to find the moment of a force?

Answer 14

moment = Fx
moment = force x perpendicular distance from the point of rotation

Question 15

How would you find the perpendicular distance from a pivot if the force isn’t perpendicular?

Answer 15

x = (length of lever in m) x cosθ
∵ moment = F x (length of lever in m) x cosθ

Question 16

State the principle of moments

Answer 16

The principle of moments states that: When a body is in equilibrium, the net force acting on it is zero and its net moment is zero. This means that when an object is in equilibrium, its clockwise and anticlockwise moment are equal and opposite to each other.

Question 17

What is a couple?

Answer 17

A pair of equal and opposite forces that are parallel to each other and the same distance away from the pivot as each other. This will make the object spin without the pivot moving.

Question 18

How would you find the torque?

Answer 18

torque of a couple = one of the forces x perpendicular separation between the 2 forces

Question 19

How would you describe an object that is in equilibrium?

Answer 19

The object will have no resultant forces so will not accelerate in any direction.

Question 20

State the equation to find density

Answer 20

ρ = m/V
density = mass / volume

Question 21

State the equation for pressure

Answer 21

p = F/A
pressure = force / area

Question 22

What is density?

Answer 22

The amount of mass per unit volume for example the amount of grams in 1m³

Question 23

What is the unit for pressure?

Answer 23

Pa or N/m²

Question 24

State the equation for pressure in a vertical column of liquid

Answer 24

p = hρg
pressure = height of liquid column x density of liquid x gravitational field strength

Question 25

State the equation for upthrust

Answer 25

upthrust = Axρg
upthrust = Vρg
upthrust = volume x density of fluid x gravitational field strength