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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?
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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.
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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.
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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