STATE COUNCIL OF EDUCATIONAL RESEARCH AND TRAININGTELANGANA, HYDERABAD

ACADEMIC YEAR- 2020-21, LEVEL – 2

Class: VIII Medium: English Subject: Physical Science

Name of the chapter : Force Worksheet No.3

Topic / Concept: Field Forces and Contact Forces

KEY CONCEPTS1. Types of forces.2. Field force and Contact force.

LEARNING OUTCOMES Students....1. Able to understand the concept of field force and could give examples for it.2. Able to write the differences between field force and contact force.3. Could understand and apply the uses of different types of forces in day to day

life.4. Able to form hypotheses for field force, gravitational force and electronic force.5. Able to perform activities related to field force, gravitational force and electronic

force.The force which occurs without any physical contact between two objects is known as a force at a

distance or field force. Field forces are of three types, they are:1. Magnetic force.

2. Electrostatic force.

3. Gravitational force.

Let us understand magnetic force:.

Magnetic force:A magnet can attract or repel another magnet without any contact. This invisible force of attraction or repulsion between two magnets is called magnetic force. Magnetic force is a field force. This force can also exist between a magnet and magnetic materials (like iron).

Activity -1(Understanding magnetic force)1. Take a bar magnet and keep it on the table. 2. Take a magnetic compass needle and keep it near the bar magnet. 3. What will happen if the needle is brought closer to the magnet ? Guess.4. As soon as the needle is brought closer to the magnet, it will get attracted by the magnet.5. Why does the bar magnet attracts the needle placed nearer to it?6. How far the needle to be kept to get attracted by the magnet?7. Up to what extent around the magnet is this force of attraction present?

Let us see another activity: Activity-2: Visualizing a magnetic field1. Take a bar magnet and place it on a table. 2. Place a thick white paper over it (White drawing

sheet).3. On the paper, sprinkle fine powder of iron

(iron filings).4. Tap the table or the paper gently with

apen/pencil. 5. What do you observe? Do you find any pattern

of iron filings there? 6. This pattern represents magnetic field around the bar magnet.7. You can see that in a small space around the magnet, iron filings set themselves in a pattern

because they are affected by the magnetic force of the fieldcreated by the bar magnet. 8. The space around the magnet where its influence (force) can be detected is called magnetic field. 9. The magnetic field is three dimensional.

Magnetic force of lines

Electrostatic force

The force exerted by a charged body on another charged body is known as electrostatic force

Let’s perform an activity to understand electrostatic force.

Activity -31. Take a balloon, inflate it and tie up the open end.2. Now cut a paper into small pieces and place them on the

floor. 3. Rub the balloon with a paper and bring the balloon near the

pieces of papers. 4. What happens now? Are the bits of paper pulled towards the

balloon? 5. Why does the balloon attract the pieces of paper? 6. We can say that when the balloon is rubbed with a paper, it acquires an electrostatic charge on its

surface.

7. The balloon is now said to be a charged body. 8. When it is brought near the bits of paper, the pieces acquire opposite charge and will rise and

cling to the balloon.

Gravitational forceWhat happens if an object is thrown upwards?What happens if we drop a ball in the air from the top of a building?Why do the fruits fall down from a tree?

In all of the above examples,some force is acting on the objects.

If an object is thrown upwards, there exists a force which pulls it down towardsthe earth, because of this it falls down to the ground. We call this force as Gravitational force.

1. Every object on the Earth or close to Earth will experience a

gravitational pull.

2. This force of gravity (gravitational force) exists not just

between the earth and objects on it but also between any two

bodies (or masses) present everywhere in the universe.

3. The earth is so massive and huge compared to all other objects

on it.

4. So all the other objects close to the earth are attracted or pulled towards it.

5. Gravitational force works even the objects are not in contact. So, this is a field force.

ASSESSMENT

ANSWER THE FOLLOWING QUESTIONS:

1. List out the required material to conduct an activity to understand the electrostatic force and write

the procedure?

2. Explain the experimental procedure to understand the magnetic field?

3. Draw the diagram of magnetic lines of force around a bar magnet?4. How do you charge a balloon?5. Write any two situations of gravitational force observed in day to day life.

MULTIPLE CHOICE QUESTIONS:1. The attraction or repulsion between two objects is known as ( )

A) Electrostatic force B)Gravitational forceC) Muscular force D) Contact force

2. The space around the magnet where its influence can be detected is called ( )A) Magnetic field B)Electrostatic force B) Gravitational force D)Muscular force

3. The reason for the attraction of pieces of paper by the balloon is ( )A) Electrostatic force B)Gravitational forceC) Magnetic force D) Contact force