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Define the following terms:
(i) Inertia
(ii) Momentum
(iii) Force
(iv) Force of friction
(v) Centripetal force
(i) Inertia:
The inertia of a body is its property due to which it any change in its state of rest or motion.
Galileo related the inertia of a body with its mass; the greater is the mass of a body greater its inertia.
Inertia $\propto$ mass of the body
(ii) Momentum:
The momentum of a body is the quantity of motion it possesses due to its mass and velocity.
The momentum P of a body is given by the product of its mass m and velocity v. Thus
P = mv
Momentum is a vector quantity. Its SI unit is $kgms^{-1}$
The momentum of a system depends on its mass and velocity.
(iii) Force:
A force moves or tends to move stops or tends to stop the motion of a body. The force can also change the direction of motion of a body.
F = ma
Si unit of a force in the newton.
Note: A force can also change the shape or size of a body on which It acts.
(iv) Force of friction:
Friction:
The force, that opposes the motion of moving objects is called friction.
Friction is a force that comes into action as soon as the body is pushed or pulled over a surface.
Factor on which friction depends:
In the case of solids, the force of friction between two bodies depends upon many factors such as the nature of the two surfaces in contact and the pressing force between them.
(v) Centripetal force:
Centripetal force is a force that keeps a body moving in a circle.
The centre-seeking force is called the centripetal force. It keeps the body moving in a circle. Centripetal force always acts perpendicular to the motion of the body
$Fc =\frac{mv^2}{r}$
Differentiate between mass and weight.
Mass and weight:
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Mass |
Weight |
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1.The quantity of matter contained in a body is called its mass. |
1.Weight is a force with which earth attracts a body towards its centre. |
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2.The mass of a body remains constant everywhere, whether it is measured at a point far away from the centre of the earth, or the surface at the centre of the earth. |
2.The weight of a body is not a constant in quantity but its value is different at different places. |
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3.Mass is a scalar quantity. |
3.Weight is a vector quantity and is always directed towards the centre of the earth. |
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4.The SI unit of mass is kilogram. |
4.The SI unit of weight is newton. |
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5.Mass is measured by ordinary balance. |
5.weight is measured by spring balance. |
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6.Mass of the body cannot be zero. |
6. The weight of the body can be zero i,e at the centre of the earth and in space where g=0 so w=mg=m×0=0 |
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7. It is the measure of inertia in a body i.e: m= |
7. Weight is given by w=mg |
What is the difference between:
Action and reaction
Action and reaction:
Newton’s third law of motion deals with the reaction of a body when a force act on it. Let body A exerts a force on another body B. Body B reacts against this force and exerts a force on body A. The force exerted by body A on B is the action force whereas the force exerted by body B on A is called the reaction force.
Note that action and reaction forces act on different bodies.
Example:
Action and reaction forces act on different objects and in opposite directions. For example, if the rocket pushes the gas out, the gas pushes back against the missile. The forces on different objects (the gas, and the rocket, respectively), and in opposite direction.
