Killina Presentation Secondary School

Mechanics Definitions

Displacement is distance in a given direction.

Speed is the rate of change of distance with respect to time.

Velocity is the rate of change of Displacement with respect to time.

Acceleration is the rate of change of Velocity with respect to time.

A Scalar Quantity is one which has magnitude only.

A Vector Quantity is one which has both magnitude and direction.

A Force is that which can cause an acceleration.

The Newton is that force which gives a mass of one kg an acceleration of 1 ms.

Friction is a force which opposes the relative motion between two objects.

The weight of an object is the force of the Earth’s gravity acting on it.

Momentum is the product of Mass times Velocity.

Newton’s First Law of Motion states that every object will remain in a state of rest or travelling with a constant velocity unless an unbalanced external force acts on it.

Newton’s Second Law of Motion states that the rate of change of an object’s momentum is directly proportional to the force which caused it.

Newton’s Third Law of Motion states that if an object A exerts a force on an object B, then B will exert an equal but opposite force on A.

The Principle of Conservation of Momentum states that in any collision between two objects, the total momentum before impact equals total momentum after impact provided no external forces act on the system.

The Density of a substance is a measure of its mass per unit volume.

Pressure is defined as Force per unit Area.

Archimedes’ Principle states that when an object is immersed in a fluid, the upthrust it experiences is equal to the weight of the displaced fluid.

The Law of Flotation states that the weight of a floating object is equal to the weight of the fluid it displaces.

Boyle’s Law states that at constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure.

Newton’s Law of Gravitation states that any two objects in the universe are attracted to each other with a force that is directly proportional to the product of their masses, and inversely proportional to the square of the distance between them.

The Moment of a Force is equal to the force multiplied by the perpendicular distance between the force and the fulcrum.

Conditions for Equilibrium of an object under Coplanar Forces.
If an object is in equilibrium then:
The vector sum of the forces in any direction is zero.
(forces up = forces down)
The sum of the moments about any point is zero.

Work is defined as the product of Displacement by Force (in the direction of the displacement).

Energy is the ability to do work.

The Principle of Conservation of Energy states that Energy cannot be created or destroyed but can only be converted from one form to another.

Power is the rate at which work is done.
Or
Power is the rate at which energy is converted from one form to another.

Angular Velocity is the rate of change of angle with respect to time.

The force - acting in towards the centre - required to keep an object moving in a circle is called Centripetal Force.

Hooke’s Law states that when an object is stretched the restoring force F is directly proportional to the displacement – provided the elastic limit is not exceeded.