Force

Unit 3

FORCE

Learning Objectives

After learning this lesson, students will be able to

* define movements and actions

*define force

* know different types of forces

* know the force of friction

* understand the need and significance of frictional force

1. Simple movements and actions

In our daily life, we do different actions such as pushing, pulling, twisting and turning. By doing these actions we move or change the shape of an object.

* Change in position of an object is called movement.

* Action is the motion which gives the required result.

Let us look at the pictures below to understand movement and action better

The player hits the ball with hockey stick,

Boys are riding bicycle.

In the above pictures,

What moves?

The ball, The cycle.

What is the action?

Hitting the ball , Riding the bicycle.

Motion

When an object or a thing moves from one place to another, it is said to be in motion.

Let us speak

2. Force

Force is a push or a pull on an object which make it move, changes its shape or stops it from moving.

* Force involves an interaction between two or more objects.

* Force can lift or drop an object.

Without force, we can‛t move any object.

Observe and Discuss

1. Push

Look and say: What kind of actions do the pictures denote?

Here, all the pictures show pushing action.

When a force is applied in the direction of an object, it is calles push.

2. Pull

Look and say: What kind of actions do the pictures say?

Here all the actions show pulling action.

When a force is applied in the direction opposite to the direction of an object, it is called pull.

Put a tick (✓) mark for the pictures of motion.

Classify the following - Push or Pull?

Activities - Push/Pull

1. Riding the bicycle  Push

2. Moving the table towards you Pull

3. Dragging the chair  Pull

4. Moving a car to start  Push

5. Opening the window  Push

6. Stretching the rubber band  Pull

7.  Removing the shoe laces  Pull

3. Effect of forces

Energy is needed to apply force

Force helps us to do the following things

* Force can change the direction

* Force can change the speed

* Force can stop a moving object

* Force can change the shape

Force changes direction

Here, in the picture, a boy hits the shuttlecock and it reaches the other boy. He hits it again with the racket to move it to the opposite direction.

Force changes motion

* The cycle moves forward because force is applied on the cycle by pedaling.

* When we stop pedaling the force is removed and the cycle stops and comes to rest.

Some applications of force in everyday life

Force can change the speed

Force can change the speed of a body which is already in motion by providing more force on it. Ram and his brother are playing with a toy car. Ram tries to move the toy car and his brother stops it from the opposite direction to slow down the toy car.

Thus, force changes the speed of an object.

Force can stop a moving object

An object stops moving when we apply force in the opposite direction.

* Have you played football game?

* How will you stop the ball?

* The goal keeper applies force and stops the ball.

Force can change the shape

* When an inflated balloon or water balloon is pressed, some force is applied on both sides of the balloon. Thus, it changes its shape.

* While squeezing a plastic water bottle force is applied on all sides of the bottle. Thus, the shape and size of the bottle is changed.

Do you know

Less force is required in pulling than in pushing. So it is easy to pull than push an object.

Match the following.

4. Types of force

A . Contact Force

When a force is applied by touching the object, it is called contact force.

Eg : Lighting a match stick

Contact force is classified into three.

1. Muscular force 2. Mechanical force 3. Frictional force

B . Non-Contact Force

When a force is applied without touching an object, it is called non-contact force.

Eg. Vaccum cleaner, Magnet.

Non - contact force is classified into two.

1. Gravitational force 2. Magnetic force

Muscular force

The force applied by using the parts of our body is called muscular force.

I use my legs to pedal. The force used here is muscular force.

I use my hands to make pots. The force used here is muscular force.

Mechanical force

The force applied by a machine is called mechanical force.

Example

Gravitational force

* When you throw a ball up in the air, why does it come down?

* When we jump, why do we come down? Why don’t we fly?

Why do fruits fall down from the tree?

Why this happens?

The Earth pulls all the objects towards itself. The force applied by the Earth to pull objects towards itself is called gravitational force.

Magnetic force

A magnet is a material that attracts things made of iron. The force that attracts things is called magnetic force.

Observe the picture and write the kind of force involved here.

Tick (✓) the muscular force.

Frictional force

When we roll down a ball on grass ground, it slows down and finally stops. We know that an object cannot stop without force. The force that stopped the ball is frictional force. Force exerted by the surface when an object moves over it is called Frictional force.

Think! Why do we sprinkle powder on the carom board before playing carrom?

To reduce the friction between the surface of the carrom board, the striker and the coins.

5. Friction

When we use eraser on a paper, the shape of the eraser changes. Why? It is because of the friction between the eraser and the paper.

Friction is a force actions between two surfaces in contact or when they slide over one another.

Do you Know?

Early man accidentally discovered fire by rubbing two flint stones (chikimuki kal) together. The frictional force between two stones created a spark.

List out the push activities

Swing,

Playing foot ball,

Kids scooter, cycling.

List out the pull activity

Pulling wood,

Pulling trolley,

Kiting.

List the frictions here

Sliding,

Playing in sand,

See saws.