Q1. Define Force.
Ans : Force is the push or pull needed to move something.
Q2. What are the various effects of Force?
Ans: The various effects of Force are:
(i) Force can make a stationary object move.
(ii) Force can stop a moving object.
(iii) Force can change the direction of a moving object.
(iv) Force can make a moving object move faster.
(v) Force can make a slowing object moving slower.
(vi) Force can change the shape of an object.
Q3. What do you mean by muscular force?
Ans: The force applied by the muscles of human beings and animals is called a muscular force.
Q4. Define Magnetic force.
Ans: The force applied by a magnet is known as magnetic force.
Q5. What do you mean by Gravitational force?
Ans: The force with which the earth attracts object towards itself is known as gravitational force.
Q6. What do you mean by Weight? What is its S.I unit? Which instrument is used to measure weight?
Ans: Weight is the force with which the body gets attracted towards the earth. Its S.I. unit is newton (N). Spring balance is used to measure weight.
Q7. Define electrostatic force.
Ans: The force exerted by the electric charges at rest is called electrostatic force. Due to this force electrically charged body attract or repel other objects.
Q8. What do you mean by frictional force?
Ans: The force that resists the motion of an object is called frictional force.
Q9.Write the various advantages of frictional force.
Ans: Advantages of frictional force:
(i) It is becomes difficult to walk on a slippery road due to low friction.
(ii) We cannot fix nail in the wood or wall if there is no friction. It is friction which holds the nail.
(iii) We cannot walk on ground without friction.
(iv) We cannot write on a paper with a pencil or pen without friction.
Q10.What are the various disadvantages of frictional force?
Ans: Disadvantages of frictional force:
(i) The main disadvantage of friction is that it produces heat in various parts of machines. In this way some useful energy is wasted as heat energy.
(ii) It opposes the motion.
(iii) Due to friction, noise is also produced in machines.
(iv) Due to friction, engines of automobiles consume more fuel which is a money loss.
Q11. What do you mean by a lubricant?
Ans: A lubricant is a substance that reduces friction between two moving surfaces.e.g. oil, grease.
Q12. Write various methods to reduce friction.
Ans: There are two most widely used methods to reduce friction:
(i) Using lubricants.
(ii) Converting Sliding Friction into rolling friction.
Q13. Athletes wear specially designed shoes with spikes on the soles. Why?
Ans: Athletes with use shoes spikes as they grip the ground better and thus increases the friction due to which their shoes do not slip while they run or play.
Q14. It is necessary to keep the bathroom floor clean and free of oily substances. Why?
Ans:It is difficult to walk on a soapy floor because the layer of soap makes floor smooth and thus reduces the friction. Thus the foot cannot make a proper grip on the floor and it starts getting to slip on the floor
Q15. What do you mean by contact forces?
Ans: The forces which act on bodies when they are in physical contact,are called contact forces.e.g. frictional force, Impact force
Q16. What do you mean by non contact forces?
Ans :Forces that can act from a distance are called non contact forces.e.g.gravitational force, electrostatic force, magnetic force.
Q17. .Define pressure
Ans: Pressure is defined as force acting per unit area.
Q18. State and define S.I.unit of pressure.
Ans: The S.I. unit of pressure is pascal(Pa).If a force of 1N is applied to an area of 1m2, then the pressure is 1 pascal or 1N/m2.
Q19.It is easier to cut with a sharp knife than a blunt knife.Why?
Ans: A sharp knife blade has a smaller area. Therefore for the same amount of force, the sharp knife blade exerts more pressure and cuts more easily.
Q20.When we walk on a sand our feet sink into it but a camel can easily walk on sand. Why?
Ans: A camel can easily walk on sand because a camel has broad feet.Thus the pressure exerted by its body on the sand is less.
