MAGNETIC FORCE

MAGNETIC FORCE

Activity 11.6: ( Observing magnetic force )

*   Take a pair of bar magnets.

*   Place the longer side of one of the magnets over three round shaped pencils or wooden rollers as shown in Fig.11.10.

*   Now bring one end of the other magnet near the end of the magnet placed on the rollers.

*   Make sure that the two magnets do not touch each other. Observe what happens.

*   Next, bring the other end of the magnet near the same end of the magnet placed on the rollers (Fig.11.10).

*   Note what happens to the magnet placed on the rollers every time another magnet is brought near it.

Figure 11.10: Observing attraction and repulsion between two magnets

Does the magnet on the rollers begin to move when the other magnet is brought near it? Does it always move in the direction of the approaching magnet? What do these observations suggest? Does it mean that some force must be acting between the two magnets?

You have learned in Class VI that like poles of two magnets repel each other and unlike poles attract each other. Attraction or repulsion between objects can also be seen as another form of pull or push. Do you have to bring the magnets in contact for observing the force between them? A magnet can exert a force on another magnet without being in contact with it. The force exerted by a magnet is an example of a non-contact force.

Similarly, the force exerted by a magnet on a piece of iron is also a non-contact force.

Source: This topic is taken from NCERT TEXTBOOK

ELECTROSTATIC FORCE

ELECTROSTATIC FORCE

Activity 11.7: ( observing electrostatic force )

*   Take a plastic straw and cut it into nearly two equal pieces.

*   Suspend one of the pieces from the edge of a table with the help of a piece of thread (Fig. 11.11).

*   Now hold the other piece of straw in your hand and rub its free end with a sheet of paper.

*   Bring the rubbed end of the straw near the suspended straw.

*   Make sure that the two pieces do not touch each other. What do you observe?

*   Next, rub the free end of the suspended piece of straw with a sheet of paper.

*   Again, bring the piece of straw that was rubbed earlier with paper near the free end of the suspended straw.

*   What do you observe now?

Figure 11.11: A straw rubbed with paper attracts another straw but repels it if it has also been rubbed with a sheet of paper

A straw is said to have acquired an electrostatic charge after it has been rubbed with a sheet of paper. Such a straw is an example of a charged body.

The force exerted by a charged body on another charged or uncharged body is known as electrostatic force. This force comes into play even when the bodies are not in contact. The electrostatic force, therefore, is another example of a non-contact force. You will learn more about electric charges in Chapter 15.

Source: This topic is taken from NCERT TEXTBOOK

GRAVITATIONAL FORCE

GRAVITATIONAL FORCE

You know that a coin or a pen falls to the ground when it slips off your hand. Leaves and fruits also fall to the ground when they get detached from the plant. Have you ever wondered why it is so?

When the coin is held in your hand it is at rest. As soon as it is released, it begins to move downwards. It is clear that the state of motion of the coin undergoes a change. Can this happen without a force acting on it? Which is this force?

Objects or things fall towards the earth because it pulls them. This force is called the force of gravity, or just gravity. This is an attractive force. The force of gravity acts on all objects. The force of gravity acts on all of us all the time without our being aware of it. Water begins to flow towards the ground as soon as we open a tap. Water in rivers flows downward due to the force of gravity.

Gravity is not a property of the earth alone. In fact, every object in the universe, whether small or large, exerts a force on every other object. This force is known as the gravitational force.

Source: This topic is taken from NCERT TEXTBOOK