Laws of Motion Standard 9 Force A push

Laws of Motion Standard 9

Force A push or pull that can cause an object to change its velocity or which can cause a flexible object to deform.

Balanced Forces Force F 1 Force F 2 F 1 and F 2 are acting on the rope. If both teams are evenly matched then F 1 = F 2. But F 1 and F 2 are in the opposite direction and hence cancel each other. The net force on the rope = 0. When a number of forces act on a body such that the net force acting on the body is 0, then such a combination of forces are known as balanced forces.

Types of Forces Contact Forces Muscular Frictional Non-Contact Forces Magnetic Gravitational Electrostatic

Objects are Lazy – 1 Rough Ground Smooth tiled floor Football will remain at the same place unless someone kicks it. The football stops rolling after sometime as friction opposes its motion. The football travels more distance on a smooth surface as the frictional force is smaller. If there was no friction, the football would keep on rolling. First the football does not want to move and once moving it does not want to stop (unless some force is applied).

Objects are Lazy – 2 Little guy Toy vehicle What will happen when the bus hits the wall? Wall Stack of books The bus stops moving when it hits the wall. However the little guy on top of the bus continues moving and topples over.

Newton’s First Law of Motion

Newton’s Second Law of Motion

Newton’s Second Law of Motion The rate of change of momentum is directly proportional to the impressed force and takes place in the direction in which the force acts.

Newton’s Third Law of Motion Straw String Force of air on balloon pushes it forward Wall Atmospheric pressure pushes the air out As the air escapes from the balloon it pushes the balloon forward.

Newton’s Third Law of Motion Ball pushes the ground downwards Ground pushes the ball upwards When moving down, gravity acts in the direction of motion accelerating the ball. When moving up, gravity opposes the motion decelerating the ball.

Newton’s Third Law of Motion Block pushes the water downwards Water pushes the block upwards When you take off your hand the force of the water pushes the block upwards. The harder you push the block downwards, more the force with which water pushes the block back. For every action there is an equal and opposite reaction. Action and Reaction act on different bodies and hence do not cancel each other.

Conservation of Momentum If there is no net force acting on two interacting bodies then their total momentum is conserved.

Units of Measurement Physical Quantity SI Units CGS Units Force kg m/s 2 or Newton g cm/s 2 or dyne Momentum kg m/s g cm/s