Physics AS level (Chp 1 - 15) Definitions

Physics Definitions:

Acceleration: Rate of change of velocity of an object.

Constant acceleration: When the change in velocity of an object is the same over the same time period, it is also known as uniform acceleration.

Newton’s second law of motion: Resultant force is proportional to mass x acceleration.

Inertia: A measure of how difficult it is to change the velocity of an object. It’s a measure of the mass of an object; a massive object has large inertia.

Newton’s first law of motion: An object will remain at rest or in a state of uniform motion unless a resultant force acts on it.

Newton’s third law of motion: When 2 bodies interact, the forces they exert on each other are equal in size and opposite in direction.

Moment of force: Moment of force about a point is the product of force and perpendicular distance from the line of action of the force to the point.

Principle of moments: The sum of clockwise moments about a point is equal to the sum of anticlockwise moments about the same point, provided the body is in equilibrium.

Joule: Work done when a force of 1N moves a distance of 1m in the direction of the force.

Principle of conservation of energy: Energy cannot be created or destroyed. It can only be changed from 1 form to another.

Power: The power of a device is the rate at which it does work per unit of time.

Watt: 1W = 1 J/s

Linear momentum: Linear momentum of a body is the product of its mass and velocity.

Conservation of momentum: The sum/total momentum of bodies in a closed system is constant, provided no resultant external force acts.

Newton’s first law of motion: An object remains at rest/travels at constant velocity unless it is acted on by a resultant force.

Newton’s second law of motion: Resultant force on the body is proportional to the rate of change of momentum of the body.

Newton’s third law of motion: When body A produces a force on body B, then body B produces an equal and opposite force on body A.

Density: Density is mass per unit volume.

Pressure: Perpendicular force acting per unit cross-sectional area.

Archimedes’ principle: Upthrust acting on a body is equal to the weight of the liquid/gas it displaces.

Hooke’s law: Provided elastic limit is not exceeded, the extension of the object is proportional to the applied force.

Strain: Extension per unit length

Stress: Force per unit cross-sectional area that acts at right angles to a surface.

Young modulus: Stress in the material divided by strain.

Potential difference: The potential difference between 2 points is the energy transferred per unit charge as it moves from point A to B.

E.M.F: Energy transferred per unit charge in driving a charge round a complete circuit.

Electrical resistance: Ratio of potential difference to current.

Kirchhoff’s first law: The sum of currents entering any point in a circuit is equal to the sum of currents leaving that point.

Kirchhoff’s second law: The sum of E.M.Fs around any loop in a circuit is equal to the sum of potential differences around the loop.

Ohm’s law: A conductor obeys Ohm’s law if current is directly proportional to potential difference across its ends.

Ohmic: Component that obeys Ohm’s law.

Non-ohmic: Component that does not obey Ohm’s law.

Unified atomic mass unit: 1/12 th of the mass of a carbon-12 atom.

Principle of superposition: When 2 or more waves meet at a point, the resultant displacement is the sum of the displacements of individual waves.

Electron volt: 1 eV is the energy transferred when an electron travels through a potential difference of 1 volt.