4th Class Science Force, Work and Energy Force

     Introduction

To do any kind of work we have to apply force and to apply force we require energy. It shows that these three terms (Work, Force and Energy) are related and dependent on one another.

Work                                     Force                                     Energy

Done      <—————            Applied       <—————      Needed

Thus we can say that work is only done, when we have the energy to apply force.

       Force

Think of the normal activities like catching a ball, throwing a ball, pulling or pushing a chair. Have you ever thought, why a chair moves when we push it or pull it? The chair moves because we apply a force on it.

Force is push or pull acting on an object. Force is used not only to move an object, but also to stop it. Force is also used to change the direction and position of an object. It is also used to increase or decrease the speed of moving object. While playing cricket, many of you must have been given caught out. The friend of yours who caught the ball has applied force to stop the ball, which was moving in the air by your hitting. The force applied by you is to move the ball and the force applied by your friend is to stop the ball. Both you and your friend has applied force but to do different kinds of work.

Force is applied to hit the ball

Every one of you must have enjoyed your bicycle ride. You can increase or decrease the speed of the bicycle when you want to. The speed of the bicycle depends on the rider. The rider apply force to increase or decrease the speed of the cycle.

Force is used to increase or decrea.se the speed of moving object. Children, while playing with football or basketball have the habit of sitting on it or pushing it against the hard surfaces. While doing so shape of ball gets changed. Force is use to change the shape of the object. Therefore, force is push or pull acting on an object. Force is used to move objects, to stop the moving object, to change the direction of the moving object, to decrease or increase the speed of the object and also to change the shape of the object.

     Force applied can make the ____________.

(a) Body move

(b) Body stop

(c) Change the direction of motion

(d) Change shaped

(e) All of the above

Answer: (e)

Explanation 

Force applied can move the object, stop the moving object, change the direction of motion, and change the shape of the object.

     Which one of the following statements is correct?

Statement 1: Force is used to increase or decrease the speed of a moving object.

Statement 2: Force is not used to increase or decrease the speed of a moving object.

(a) Statement 1

(b) Statement 2

(c) Both statements are correct

(d) Both statements are incorrect

(e) None of these

Answer: (a)

Explanation 

Force is used to increase or decrease the speed of an object..