Lss module 1 chpt 1 investigating forces

MODULE 1:GADGETS WORK WONDERS (I)Chapter 1 Exploring Forces

© Copyright Star Publishing Pte Ltd

Chapter 1 Exploring Forces

1.1 What are the effects of forces?

1.2 How can forces be measured? 1.3 What are the effects of friction? 1.4 How do simple machines work?


ObjectivesState that a force can change the shape,

size, state of rest and motion of a body

Give examples of different forces: pushing, lifting, stretching, twisting, pressing, gravitational, frictional and magnetic forces

Infer the effects of forces such as◦change in state of rest and / or motion of a body◦change in shape and / or size of a body


What is a force? A force is a push

or a pull.

Actions such as lifting, stretching, bending, twisting and squeezing involve pushing and pulling.


Actions Involving PushingActivity Book LinkActivity 1.1Forces in Daily Life


Actions Involving Pulling


Actions Involving Pushing and Pulling

Other examples of forcesOther examples of

forces are frictional force, magnetic force and gravitational force.


How is life in space without any gravitational pull?

What is frictional force?Friction is the

force that acts between two surfaces in contact.

When we hold a glass of water, there is friction between our hand and the glass.


What is magnetic force?A magnetic

force is the force between two magnetic poles.

It can be an attractive or a repulsive force.


Magnetic forces are useful in many areas of our lives.

What is gravitational force?Gravitational

force is the force that pulls an object towards the earth.


Gravitational force helps in daily tasks such as pouring

water from a jar.

What are the effects of forces?A force can

change the shape and/or size of an object.


crushing a tin can changes itsshape and size

squeezing a sponge can changes itsshape and size

What are the effects of forces?A force can change the motion of an object;

for example,

(i) move a stationary object,

(ii) stop a moving object,

(iii) change the speed of a moving object,

(iv) change the direction of a moving object.© Copyright Star Publishing Pte Ltd


a force can cause a stationary ball to move

a force can make a moving ball roll fasteror slower

a force can cause a ball to change direction


1.1 What are the effects of forces? 1.2 How can forces be

measured? 1.3 What are the effects of friction? 1.4 How do simple machines work?


ObjectivesUse a spring balance to measure

force

Use newton as the unit of force


How are Forces Measured?Forces are

measured using spring balances.

The International System of Units (SI unit) of force is the newton (N). © Copyright Star Publishing

Pte Ltd

an extensionspring balance

Spring balances The two types of spring

balance are:

(a) extension spring balance(b) compression spring balance

In an extension spring balance, the force causes the spring to become extended or longer.

In a compression spring balance, the force causes the spring to be compressed or become shorter. © Copyright Star Publishing

Pte Ltd

is the force exerted by the food on the compression

spring balance a push or a pull?

How do we read a spring balance?

The size of the force can be read from the scale of a spring balance.

The reading on the scale shown is 50 N.© Copyright Star Publishing Pte Ltd

What is weight?Weight is the

force of gravity pulling an object towards the Earth.

Weight is not the same as mass.


an electronic balance is used to measure mass

Activity Book LinkActivity 1.2Making a Spring BalanceActivity 1.3Measuring Forces

Differences between weight and mass



1.1 What are the effects of forces? 1.2 How can forces be measured? 1.3 What are the effects of

friction? 1.4 How do simple machines work?


ObjectivesDescribe the effects of friction on

the motion of an object


What is Frictional Force?

Friction is a force which opposes motion.

It acts between two surfaces in contact.


friction causes a rolling ball to slow down and stop

What are the Factors Affecting Friction?Friction depends

on:

(a) the smoothness of the two surfaces in contact.

(b) the force pressing the twosurfaces together.


a carrom seed moves easily across asmooth carrom board

a heavy box on the right experiences a larger friction than an empty one

Does the Surface Area in Contact Affect Friction?

Friction does not depend on the surface area in contact.

A rectangular block experiences the same amount of friction no matter which side it is placed on a surface.


Activity Book LinkActivity 1.5Friction and Area in Contact

Is Friction a Useful Force?

Friction helps us to walk without slipping. Friction is needed for braking.Friction helps us to grip things


walking on smooth ice can make you fall brake pads on a bicycle help it

to slow down and stop

friction helps a person to grip a pencil

Is Friction a Nuisance?

Friction can also be a nuisance as it produces unwanted heat in machines and causes wear and tear.

Friction can be reduced by:(a) Using lubricants(b) Using ball bearings


lubricants and ball bearings reduce friction between moving parts of machines


1.1 What are the effects of forces? 1.2 How can forces be measured? 1.3 What are the effects of friction? 1.4 How do simple machines

work?


ObjectivesIdentify the different types of simple

machines (levers, inclined planes and pulleys) and give everyday examples of their use

Investigate the effort used when the following is used to raise a load

▲ Lever▲ Inclined plane▲ Pulley


How do Simple Machines Help Us do Work?

A simple machine is a device that makes work easier for us. It can:

(a) reduce the force needed to move a load,

(b) change a small movement into a large one,

(c) change the direction or position of a force.


examples of simple machines

Types of simple machinesThree common

types of simple machines are:

(a) levers,(b) inclined planes,(c) pulleys.


a screwdriver acts as a lever to help

open a tin of paint

Lever system

There are three parts in a lever system:(a) the fulcrum (b) the effort (c) the load.


Why is it easier to open a tin of paint with a long screwdriver than a short one?

The further the effort from the fulcrum, the smaller the effort needed to move the load.


Classes of leversThere are three

classes of levers:◦ 1st class lever

(Fulcrum is between load and effort)

◦ 2nd class lever (Load is between effort and fulcrum)

◦ 3rd class lever (Effort is between load and fulcrum)


1st class lever

2nd class lever

3rd class lever

Examples of the three classes of levers


How do levers make work easier?First and second class levers make

work easier by allowing us to use a small effort to overcome a large load.

Third class levers enable a small movement of the effort to result in a large movement of the load.

This makes work such as sweeping the floor faster. However, an effort larger than the load is needed.


What is an inclined plane?

An inclined plane is a flat surface with one end higher than the other.


a wheelchair ramp is an example of inclined plane

worker moving goods up an inclined plane into a

truck

How does an inclined plane make work easier?Moving a load up an

inclined plane requires a smaller effort than lifting the load vertically.

However, the load has to be moved over a longer distance along the inclined plane.


Activity Book LinkActivity 1.7Inclined Planes

What is a Pulley?A pulley is a wheel with a

groove for holding a rope or a cable in place.

In a single fixed pulley system, the effort needed is equal to the load. However, it is still considered a simple machine because it makes work easier.

Pulleys are also used in construction cranes, cable cars, window blinds and yachts (to raise sails).


a flag pole uses a pulleyActivity Book LinkActivity 1.8 Pulley Systems

Useful applications of pulleys


construction crane

cable car

window blinds

yacht

Lss module 1 chpt 1 investigating forces

Education

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