IB Physics Glossary

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Law of conservation of momentum

states, the total momentum of an system remains constant if no external forces act on the system.

Kinetic energy

is the energy of a moving object.

Potential energy

is a stored form of energy available to do work.

Elastic collisions

occur when the total kinetic energy of a system remains constant.

Law of Conservation of Energy

states, energy cannot be created or destroyed but is converted from one form into another or the total amount of energy in the universe is constant.


is the force of gravity acting on a mass: W=m g, m is the mass, g is the gravitational field strength \equiv acceleration due to gravity.
Its value does change with the strength of gravity. Identical objects on Earth and on the Moon have different weight values. Its SI unit is the Newton (N).

Uniform acceleration

occurs when the acceleration a is held constant.
Since acceleration is a vector quantity, constant implies a uniform magnitude and direction for the acceleration. The equations of uniform acceleration are

v=u + at (not given on IB Physics Data Booklet)

s = \frac{u+v}{2} t

s=ut + \frac{1}{2} a t^2

v^2=u^2 + 2 as

where u is the initial velocity, v is the final velocity after time t, a is the acceleration and s is the displacement.


is the amount of matter or substance inside an object.
Its value does not change with the strength of gravity. Identical objects on Earth and on the Moon have identical masses.

Log-log plots

are used to find the value of the exponent n and coefficient a for the general relationship  y= a x^n.
The value of the gradient for the log-log plot equals n and a= log^{-1}{(\text{y-intercept})}.
For example
A linear relationship should have n \approx 1;
A square-root relationship should have n \approx \frac{1}{2};
A quadratic relationship should have value n \approx 2;
An inverse-square relationship should have value n \approx -2.

Vector quantites

have magnitude and direction. Direction or changes in direction have an effect on vector quantities. Examples include displacement, velocity, acceleration, force, momentum and field strength.

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