Force and Laws of Motion

Tutormate > CBSE Syllabus-Class 9th Physics > Force and Laws of Motion

02 Relation Between Force and Motion

  • Force and motion are related and force is the cause of motion, as force affects the state of motion of an object.
  • An object moves when some force acts on it or has acted on it which produced this motion.
  • Motion can either be described as
    • Change in speed, or
    • Change in direction.
  • From the studies of Sir Isaac Newton, three conclusions can be made on force and motion:
    • Force can cause a body to accelerate
    • Force can cause a body to change directions
    • Force can cause a body to decelerate

FORCE CAN CAUSE A BODY TO ACCELERATE

    • A body at rest starts moving when a force is applied to it, provided that there is no greater force opposing it.
    • For example, when a bowler throws a ball, it starts to move forward from its initial position of rest in his hands.
    • When something begins to move from a state of rest, it accelerates. Acceleration can be described as the positive change in velocity over a period of time.
    • If force is applied in the same direction of movement of a moving object, it accelerates. For example, rotating the pedal of a bicycle will make it go faster.

FORCE CAN CAUSE A BODY TO CHANGE DIRECTIONS

    • An object changes motion when force is applied on it in an angle different to its direction of motion. Almost every ball game uses this principle.
    • The speed can be maintained if the force is applied in a perpendicular angle but the velocity will change

FORCE CAN CAUSE A BODY TO DECELERATE

    • If force is applied on the opposite direction of a moving object, it will decelerate or slow down and eventually stop altogether if the force is continued to be applied.
    • For example, when a goalkeeper stops a ball, he causes it to decelerate and stop.

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