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Lesson Objectives• Understand the terms - Lever, Fulcrum, Turning effect, Moment
• Recall the formula M= Fd and be able to calculate the moment of a force
• Be able to explain why an object with forces acting on it isn’t turning
• Be able to explain why an object at rest doesn’t turn.
• Be able to calculate the size of a force (or it’s perpendicular distance from
a pivot) acting on an object that is balanced
• Explain, in terms of forces, why objects with pivot points appear at rest or are moving in various situations.
• calculate the size of a force (or it’s perpendicular distance from a pivot) acting on an object that is balanced in a number of contexts.
• Understand equilibrium and the Law of the Lever.
• Be able to carry out simple calculations using a lever.
Turning Effects
When we apply a force, it sometimes causes an object to turn or twist.
• This turning effect of a Force is called the
Moment (M)
i.e. opening a bottle, turning a spanner
• The turning effect can be increased by
- increasing the size of the force
- increasing the distance from the turning point
A Lever is a rigid body free to move about a fixed point called the fulcrum.
• Levers are machines used to increase force. They are
called "simple machines" because they have only two parts
- the handle and the fulcrum.
• In a lever a force called the EFFORT is used to overcome a resisting force called the LOAD.
• The pivotal point is called the FULCRUM.
What is a Lever?
Types of Levers
• There are three main types of levers
– First Class Lever
– Second Class Levers
– Third Class Levers.
• In each type the fulcrum, effort and load are located at difference positions.
A First Class LeverThe First class lever is a very common type of lever.
The fulcrum is in the centre with the effort and load on the outside.
Examples of first class levers include: A seesaw, pliers, scissors.
LoadEffort
Fulcrum
Second Class Lever
A second class lever is one in where the load is in the centre and the effort and fulcrum on the outside.
Examples include a Wheelbarrow, nutcracker, and bottle opener.
Load
Effort
Fulcrum
Third Class Lever
Third class levers are hard to find. They have the effort in the centre and fulcrum and load on the outside.
Examples include Hammers and fishing rods.
Load
EffortFulcrum
Law of Moments
The Turning effect or ‘Moment’ of a force depends on the size of the force and the
distance from the fulcrum.
Moment = Force x Perpendicular distance (from the fulcrum)
M = F(N) x d(m)
The Law of the Lever
F1
F2
F1d1 = F2d2
When a body is in equilibrium the sum of the clockwise moments is equal to the sum of the anti-clockwise moments
about the same point.
When a body is in equilibrium the sum of the clockwise moments is equal to the sum of the anti-clockwise
moments about the same point.
Weight = Force
W = F
The prove the law of the lever
1. Draw diagram of equipment in copy
2. Copy table below
3. Carry out three calculations to test the law of the lever
F1 d1 F2 d2F1d1 F2d2
(N) (m) Nm (N) (m) Nm
Law of the Lever
25cm
20cm
20N F
F1 d1 = F2 d2
20N X 0.25m = F2 x (0.20m)
5Nm = F2 x (0.20m)
5Nm / 0.20m = F2
25Nm = F2
Law of the Lever
25cm
10cm 30cm
10N20N W
(0.25m x 20N) + ( 0.10m x 10M) =
5Nm + 1Nm
6Nm
6Nm / 0.30m
20N =
(W x 0.30)
W
Law of the Lever40cm
d
20N 50N
(20N x 0.4m) =
8Nm
8Nm/50N =
0.16m =
Position is at the 66cm Mark
(50N x d)
d
d
Summary• This turning effect of a Force is called the Moment (M)
Moment = Force x Perpendicular distance (from the fulcrum)
• The turning effect can be increased by increasing the size of the force or the distance from the turning point.
• A Lever is a rigid body free to move about a fixed point called the fulcrum.
• Levers are machines used to increase force. They are called "simple machines" because they have only two parts the handle and the fulcrum.
• In a lever a force called the EFFORT is used to overcome a resisting force called the LOAD. The pivotal point is called the FULCRUM.
• The Law of the lever states thatWhen a body is in equilibrium the sum of the clockwise moments is equal to the sum of the anti-clockwise moments about the same point.
F1 d1 = F2 d2