Page 122 - ACTIVE SCIENCE 4 TOC

• Frictional force always opposes the motion of one surface across another surface.

• Muscular force is the force applied using parts of the body like arms, legs, etc.
• When an object moves by applying force, it is called work. When an object does not
move by applying force, then no work is done.

• Machines have made our life easier.

• To perform any work, we need energy.

Glossary

• Machines : Devices which have made our life easy.
• Energy : It is the ability to perform work.

• Solar energy : Energy generated from the sun.

• Wind energy : Energy generated from blowing wind.
• Geothermal energy : Energy generated from the hot springs.

Practice Time

A. Tick the correct option.

1. Pull or push refers to _____________.
a. force b. energy

c. friction d. work
2. Two surfaces have to be in contact in case of _____________.

a. frictional force b. gravitational force
c. muscular force d. energy

3. If we throw an object upwards, it always falls back on earth due to _____________.
a. frictional force b. gravitational force

c. muscular force d. work

4. Our life is made easier by _____________.
a. machines b. solar energy

c. wind energy d. geothermal energy

B. Fill in the blanks.
1. Smooth surfaces offer _____________.

2. The ability to do work is called _____________.

3. Sun is the source of _____________.
4. The energy we get from the sun rays is called _____________.

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