Maharashtra Board Class 6 Science Chapter 11 Work and Energy PDF Download

Work And Energy

Observe

1. What actions are seen in the picture?

2. Is a force being applied while doing each action?

3. In the various actions in the picture, has the object changed its original position?

In the above picture, we see that the position of some of the objects has changed. That is, these objects are displaced.

Work

When an object is displaced by applying a force on it, work is said to be done.

Teacher's Note

When you push a heavy box across the floor, work is done. The work happens because you apply force and the box moves. Think of pushing your school desk in the classroom.

Exam Trick

Remember: Work = Force + Displacement. Without movement, there is no work. If you push a wall and it does not move, you did not do work.

Points to Remember

Work happens when you use force and something moves.
More force means more work is done.
Greater distance means more work is done.
If nothing moves, then no work is done.
Work is measured in units called Joules.

Try This

1. Tie a string to an empty box, as shown in the picture.

2. Pull the box through a distance of 10 metres along a straight line.

3. Now fill the same box with 20 books.

4. Pull the box again through a distance of 10 metres in a straight line. What was your experience this time?

5. Now pull this loaded box through a straight distance of 20 metres.

6. When did you feel that more work was done?

11.2: Pulling A Box

More work is done for the same displacement, when more force is applied to do the work. If the same force is applied for more displacement, more work is done by the force.

Use Your Brain Power

1. In the above activity, which are the different forces acting on the box?

2. Is a displacement possible without a force?

3. If a force is applied with both the hands on a wall, will there be a displacement?

4. If no displacement occurs on applying a force, what does it indicate?

Teacher's Note

When you pull a heavier box, you need to use more force. This is like pushing a full water tank instead of an empty one.

Exam Trick

Remember: Force and displacement are both needed for work. If you apply force but nothing moves, no work is done.

Points to Remember

Work needs both force and movement.
More force = more work for same distance.
More distance = more work for same force.
Work and force are different things.
Pushing a wall is not work because nothing moves.

11.3: Using A Pulley

Take a pulley. Fix it at a height. Draw a string over the pulley. Tie a load of two kilograms at one end. Hold the other end of the string and pull it downwards to lift the load, first up to a height of one metre, and then up to a height of four metres. When is more work done?

When the applied force is the same, more work is done when there is greater displacement. In other words, for measuring the work, both the force and the displacement must be considered.

Teacher's Note

When you lift a bucket of water higher, you do more work. This is like lifting a bucket from the ground compared to lifting it to the roof.

Exam Trick

Remember: Greater height = more work done. Always think about both the force you use and how far you move something.

Points to Remember

Both force and displacement matter for work.
Lifting higher requires more work.
The same force with more distance = more work.
Height and distance affect how much work is done.
Work cannot be measured by force alone.

The Relationship Between Work And Energy

The boy in the picture has applied a force to the toy car. Work has been done because the force applied to the car has caused displacement. In other words, transformation of the boy's energy into work has taken place through the applied force.

Run around the ground with your friends. Can your friends run as many rounds as you can?

Do all the friends have the same capacity for running?

Your friends will complete either more or less rounds than the number of rounds you complete. The number of rounds will not be the same. Some will get tired on completing two rounds, while others will get tired on completing three or four rounds. That is to say, each one's capacity to complete rounds is not the same. You can complete only as many rounds as you have the capacity for. The capacity to do work is called energy.

Do You Know?

1. Why do you get hungry after physical exercise?

2. From where does our body get energy?

3. Why do we get tired?

Let's Try This

The units of work and energy are the same. Work and energy are both measured in the unit named Joule in S.I. (System International) units.

Teacher's Note

Energy is like the power in your body. When you run, you use energy. Your body gets energy from the food you eat, just like how a car gets energy from petrol.

Exam Trick

Remember: Energy = capacity to do work. More energy means you can do more work without getting tired. Energy is measured in Joules, just like work.

Points to Remember

Energy is the ability to do work.
Every living thing has energy inside it.
Energy comes from food for your body.
Work and energy are both measured in Joules.
Different people have different amounts of energy.

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