Key Points to Remember: Laws of Motion | Chapter 1 | 10th Science

Points to Remember: Laws of Motion

Science | Chapter 1

• Mechanics is divided into statics and dynamics.
• Ability of a body to maintain its state of rest or motion is called Inertia.
• Moment of the couple is measured by the product of any one of the forces and the perpendicular distance between two forces.
• SI unit of force is newton (N). C.G.S unit is dyne.
• When a force F acts on a body for a period of time t, then the product of force and time is known as ‘impulse’.
• The unit of weight is newton or kg f
• The weight of a body is more at the poles than at the equatorial region.
• Mass of a body is defined as the quantity of matter contained in the object. Its SI unit is kilogram (kg).
• Apparent weight is the weight of the body acquired due to the action of gravity and other external forces on the body.
• Whenever a body or a person falls freely under the action of Earth’s gravitational force alone, it appears to have zero weight. This state is referred to as ‘weightlessness’.

Impulse and Impulsive Force: Definition, Formula, and Examples | 10th Science

Impulse - Definition, Formula, Examples

Impulse

A large force acting for a very short interval of time is called as ‘Impulsive force’. When a force F acts on a body for a period of time t, then the product of force and time is known as ‘impulse’ represented by ‘J’

Impulse, J = F × t (1.7)

By Newton’s second law

F = Δp / t (Δ refers to change)

Δp = F × t (1.8)

From 1.7 and 1.8

J = Δp

Impulse is also equal to the magnitude of change in momentum. Its unit is kg m s^–1 or N s. Change in momentum can be achieved in two ways. They are:

i. a large force acting for a short period of time and

ii. a smaller force acting for a longer period of time.

Examples:

• Automobiles are fitted with springs and shock absorbers to reduce jerks while moving on uneven roads.
• In cricket, a fielder pulls back his hands while catching the ball. He experiences a smaller force for a longer interval of time to catch the ball, resulting in a lesser impulse on his hands.