Turning Forces

Turning Forces
Lesson Objective: to identify and investigate turning forces
Key Words:
Pivot
Moment
Newtonmetre
Law of Moments
Turning Forces
Equillibrium
Write
This nail, I’ve been trying to pull out, just wouldn’t budge!
TPS
Any ideas as to what I could do to help get this nail out?
Why are handles put on the edge of the door? Why not put them near the hinge?
Would you use a short or long screwdriver to open a can of paint?
Which are easier to use, long handled scissors or short handled scissors?
Levers
Forces can move objects by turning them
around a pivot.
A long bar that pivots is a lever.
Load
Force
Pivot
Levers
When you push down on one side, you are applying force. The object
on the other end (the load) moves up.
Using a lever magnifies the force and makes objects easier to move.
Force Load
Pivot
As Jane applies force to
her lever, she exerts
effort at one end. Effort
The effort (force Load

downwards) causes
the load on the other
end of the lever to
move upwards.
Jane lifts her box

upwards.
Pivot
Task 2 – Labelling levers
1. Can you use the worksheet to label the diagrams correctly with the: -
■Pivot
■Force
Draw three diagrams of your own and label these

in a similar way
Force
Pivot
Force
Pivot
Force
Force
Pivot
Pivot
● A spanner is a lever that can be used to unscrew a nut.
● The spanner exerts a moment or turning force on the
nut.
● If the moment is big enough it will unscrew the nut.

● If not, there are two ways of increasing the moment
How can we make it easier to undo the nut?
● 1. Increase the distance from the force to the

pivot
– apply the force at the end or use a longer
spanner.
If the same force is
applied over a
greater distance,
a larger moment is
produced.
● 2. Increase the force applied
– push/pull harder or get someone
stronger to do it!
If a greater force is
applied over the
same distance, a
larger moment is
produced.
How can we balance the see-saw?
Use the equipment to make the see-saw balance. See if you can identify the pattern.
Left Hand Side Right Hand Side
Mass (g) Mass (g)
Distance(cm) distance(cm)
100 5
20 5
Watch
Lets text map…..
A moment is the turning effect of a force
and the pivot is the point at which the
moment has its effect
Write
What 2 things could we change to help the hippo fly?
TPS
The two factors that affect the moment are the force applied and the distance
from the pivot.
You measure force in newtons (N) and distance in metres (m) OR centimetres (cm).
You calculate a moment in Newton metres (Nm) or Newton centimetres (Ncm).
Write
Calculate the turning force of a spanner that is 20 cm long when a
force of 13N is applied.
Moment = 13N x 20cm
Moment = 260 Ncm
Calculate the turning force of a spanner that is 30 cm long when a

force of 12N is applied.
My turn
Your turn
1. Calculate the moments of the forces in each diagram. Make sure you show your
workings correctly.
2. What is the distance from the pivot that a weight of 3.3N needs to be
placed at to produce a moment of 9.9 Ncm? Think about the units carefully.
3. A tap has a handle that is 11cm long. The moment required to turn it on is
132Ncm. Calculate the force needed to turn the tap on. Think about the units Think
carefully.
4. A man holds a fishing rod with a fish hooked. The rod length is 3.2m and
the weight of the fish is 22N. He holds the rod 30cm up from the bottom.
Calculate the turning effect he feels. Hard
Balancing moments
How is this even possible? TPS

Balancing Act - Balance | Torque - PhET
What happens when two objects, with equal weight, are

placed at equal distances from the middle of a see-saw?
Watch
The law of moments
The moment of Mia’s weight acts anti-clockwise.
The moment of Amy’s weight acts clockwise.
The law of moments states that if the clockwise moment is equal to the
anti-clockwise moment, the object will be in equilibrium (balanced).
Write
Calculating the moments of forces
To understand how objects can balance we need to be able to analyse
the moments on each side of the pivots separately.
So let’s look at each side of the PIVOT and Its MOMENTS separately
Moment = Force x Distance Moment = Force x Distance
Force = 2N PIVOT Force = 2N

Distance = 4m Distance = 3m
My turn
Moment = 2N x 4m Moment = 2N x 3m
Moment = 8Nm See-saw would turn Moment = 6Nm

anti-clockwise Your turn
A see-saw has two moments.
Calculate the moments for both sides and state which way the seesaws will
tip (clockwise or anticlockwise).
Show your working.
a.
b.
My turn
Your turn
Round
1
Moment = Force x Distance
(Nm) (N) (m)
Moment = 500 N x 10 m Moment = 550 N x 6 m
= 5000 Nm = 3300 Nm
5000 Nm – 3300 Nm = 1700 Nm

Anti-clockwise
YODA WINS
500 N 10 m 6m 550 N
Round
2
(Nm) (N) (m)
= 5000 Nm = 8400 Nm
8400 Nm – 5000 Nm = 3400 Nm
Clockwise
DARTH VADER
WINS
500 N 10 m 7m 1200 N
Round
3
(Nm) (N) (m)
= 8250 Nm = 8400 Nm
8400 Nm – 8250 Nm = 150 Nm
Clockwise
DARTH VADER
WINS
750 N 11 m 7m 1200 N
Round
4
(Nm) (N) (m)
= 24000 Nm = 8400 Nm
24000 Nm – 8400 Nm = 15600 Nm
Anti-clockwise
JABBA THE
HUTT WINS
3000 N 8m 7m 1200 N
The diagram shows a crane lifting a load. The counterweight and
the load are balanced.
(a) The load is moved away from the pivot, to the right. My turn
(i) What happens to the moment produced by the load?
(ii) What should happen to the counterweight to keep the arm
balanced? Your turn
b) A load of 5000 N is placed 8 m from the pivot.
(i) What is the moment of the load? Give the unit.

(ii) How far from the pivot must the 10000 N counter weight be
placed in order to balance the load? Think
(iii) The counterweight is placed 3 m from the pivot.
What load could now be balanced 8 m from the pivot?
Hard
Complete the mastery worksheet
Let’s prove it
Method:
1. Design 3 scenarios to test with your partner
2. Calculate the moment and make a prediction of what you think will happen.
3. Test your predictions.
4. State whether your prediction was correct.
1 position of mass on 2 positions of mass on 3 or more positions of

either side of the either side of the mass on either side of
pivot pivot the pivot
SUMMARY QUESTIONS A girl applies a force of
5N to close a door. The
handle is 0.75m from
The _______ effect of a force is called a
the hinge. Calculate the
moment. You can calculate the moment of a
moment of the force.
force by multiplying the ______ by the
______ . If the anticlockwise moments equal
the clockwise moments the object will be in
____________ . This is the ____ of moments. Design a balancing game
The ________ of an object acts through a that children can play.
point called the centre of _________. Explain, in terms of the
WEIGHT/ EQUILIBRIUM/ TURNING/ law of moments and
DISTANCE/ LAW/ FORCE/ GRAVITY centre of gravity, how to
play it.
PEER ASSESS
The turning effect of a force is called a

moment. You can calculate the moment of a 5N x 0.75m = 3.75Nm
force by multiplying the force by the distance.
If the anticlockwise moments equal the
clockwise moments the object will be in
equilibrium. This is the law of moments. The
weight of an object acts through a point
called the centre of gravity. Explain your game to a
partner, ask them to
WEIGHT/ EQUILIBRIUM/ TURNING/ judge how good it is
DISTANCE/ LAW/ FORCE/ GRAVITY based on the law of
moments and centre of
gravity. WWW/ EBI.

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Turning Forces

Lesson Objective: to identify and investigate turning forces

Would you use a short or long screwdriver to open a can of paint?

A long bar that pivots is a lever.

The effort (force Load

Jane lifts her box

Draw three diagrams of your own and label these

● If the moment is big enough it will unscrew the nut.

● 1. Increase the distance from the force to the

A moment is the turning effect of a force

and the pivot is the point at which the

moment has its effect

You calculate a moment in Newton metres (Nm) or Newton centimetres (Ncm).

Moment = 13N x 20cm

Moment = 260 Ncm

Calculate the turning force of a spanner that is 30 cm long when a

How is this even possible? TPS

What happens when two objects, with equal weight, are

Moment = Force x Distance Moment = Force x Distance

Force = 2N PIVOT Force = 2N

Moment = 8Nm See-saw would turn Moment = 6Nm

5000 Nm – 3300 Nm = 1700 Nm

(i) What is the moment of the load? Give the unit.

1 position of mass on 2 positions of mass on 3 or more positions of

The turning effect of a force is called a

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