1. Introduction

In a tug-of-war match, what are the forces present? We know that the team whom is pulling with a larger force will win the match. But how do we measure force? What are the effects of forces?

Let’s watch a video on force.

What are some things you know about forces?

We cannot see force.
We can feel the effect of forces on things.

Let’s read on for more knowledge on forces.

1.1 What are the effects of forces?

A force is a push or a pull. Sometimes, both push & pull are required for the action. Let’s watch the video & locate the push & pull.

We will continue to identify the forces: push or pull.

Baby Squeeze Face. .. You're lucky I like dead babies Or I wouldn't appreciate this!! — Squeezing baby face

Giving birth

Refer to workbook Activity 1.1 [Page 1] – Forces in daily life

Refer to workbook Activity 1.2 [Page 3] – Making a spring balance

Refer to workbook Activity 1.3 [Page 6] – Measuring Forces

Let us now investigate the different types of forces: Frictional force [Friction], Magnetic force & Gravitational force [Gravity].

Frictional Force [Friction]

Friction is the force that acts between two surfaces in contact. Friction opposes motion, or we can say friction is in the opposite direction as the motion.

Image result for nuisance friction — Friction opposite in direction as the motion.

Friction can be a useful force.

Friction helps us to walk without slipping.

Friction is needed for braking or slowing down.

Using of ‘gym chalk’ to absorb moisture, perspiration & increase friction.

Friction can be used to create fire.

Friction can also be a nuisance.

Blisters on your toe caused by friction between toe & shoe.

What are the factors that will affect friction?

1. Smoothness of the surfaces in contact.

Powder is spread across the carrom board to make the surfaces smooth for both the board & the seed. In this way, friction is reduced.

When both surfaces are rough, there will be a lot of friction between. For instance, sand paper against a piece of wood.

2. Friction depends on the force pressing on the two surfaces.

Who will be receiving more friction? The child or the adult?

The heavier object will experience a larger friction compared to the lighter object.

3. However, friction does not depend on the amount of surface area in contact.

No matter how you place the object is whichever surface, the amount of friction remains the same.

Let us look at some ways to reduce friction.

Image result for reduce friction ball bearings — (b) using rollers or ball bearings

Refer to workbook Activity 1.4 [Page 8] – Effect of friction on motion

Refer to workbook Activity 1. [Page 10] – Friction and area in contact

Magnetic force

Magnetic force is the force between two magnetic poles. It can be an attractive or a repulsive force.

Let’s watch the video to understand more.

After watching the video, answer these questions:

When do magnets attract each other?
When do magnets repel each other?
What are the metals that magnets attract?

[Tip: CoINS which stands for Cobalt, Iron, Nickel, Steel]

We shall investigate how magnetic forces are useful in our lives.

Gravitational Force [Gravity]

Gravitational force [gravity] is the force that pulls an object towards the earth. Without gravity, we will not be able to do many things.

How is life like without gravity?

Quiz Time

1. Identify the following forces:

(a) The force used to light up a match stick.

(b) The force that changes the direction of a compass.

(d) The forces that cause raindrops to fall from the sky.

(e) The forces that brakes a rotating wheel.

Effects of Forces

Forces are invisible but their effects can be observed.

(a) A force can change the shape and/or size of an object:

(b) A force can change the motion of an object:

1.2 How can forces be measured?

Forces are measured using spring balances

There are two types of spring balance:

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

In compression spring balance, the force causes the spring to be compressed or shorter. The greater the force, the shorter the spring.

The SI unit [International System of Units] of force is Newton (N).

Weight is a kind of force that we experience everyday. Weight is the force of gravity pulling the object towards the earth. However, it is always confused with mass.

Weight	Mass
Force	Not a force
Pull of gravity on the object	Amount of matter in the object
SI unit – Newton (N)	SI unit – kilogram (kg)
Measured with spring balance	Measured with electronic balance

This is a video of what you have learnt so far, you can stop at timing 2.27 min:

1.4 How do simple machines work?

Simple machines make work easier for people. How does it make work easier?

(a) Simple machines reduce the force needed

(b) Simple machines change a small movement into a large movement

There are three types of simple machines:

Levers

There are three parts in a lever system:

(a) **Effort** – force applied (b) **Fulcrum** – fixed point where the lever turns (c) **Load** – force to be overcome

There are three classes of levers, and they are grouped according to which part is placed in the center.

First – Fulcrum, Second – Load, Third – Effort

First and second class levers makes work easier by allowing us to use a small effort to overcome a large load.

However, for third class levers, a small movement of the effort will result in a large movement of the load. This makes work faster but larger effort is needed.