Force, Turning Effects, and Pressure Vocabulary

Vocabulary flashcards based on Middle School Physics lecture notes covering fundamental concepts of force, units of measurement, turning effects, moments, and thrust.

Rest (or Stationary Body)

The state of a body when it does not change its position with respect to its surroundings.

Motion (or Moving Body)

The state of a body when it changes its position with respect to its surroundings.

Force

That cause (push or pull) which changes the state of a body (either the state of rest or the state of motion) or changes the size or shape of the body.

Speed

The distance travelled by a body in one second.

Newton ($N$)

The S.I. unit of force, named after Sir Issac Newton. It is defined as the force which when applied on a moving body of mass $1\,kg$ in the direction of its motion, increases its speed by $1\,m$ in one second.

Weight (or Force of Gravity)

The force of attraction exerted on a body by the earth.

Kilogram Force ($kgf$)

The gravitational unit of force defined as the force of gravity on a body of mass $1\,kg$ at a place, related to newtons as $1\,kgf = 10\,N$ (nearly) or precisely $1\,kgf = 9.8\,N$.

Rigid Body

A body in which the inter-spacing between its constituent particles does not change when a force is applied on it.

Non-Rigid Body

A body in which the inter-spacing between its constituent particles changes when a force is applied on it.

Axis of Rotation

The vertical axis passing through a pivoted point $O$ about which a body turns when a force is applied.

Moment of Force (or Torque)

The product of the magnitude of the force and the perpendicular distance of the force from the pivoted point.

S.I. Unit of Moment of Force

Newton $\times$ metre, written in short form as $N\,m$ (not written as joule).

C.G.S. Unit of Moment of Force

Dyne $\times$ cm, written in short form as $\text{dyne}\,cm$.

Anticlockwise Moment

The turning effect on a body that rotates it in an anticlockwise direction, conventionally taken as positive.

Clockwise Moment

The turning effect on a body that rotates it in a clockwise direction, conventionally taken as negative.

Thrust

The force acting normally (perpendicularly) on a surface.