definitions

principle of homogeneity

equations which are governed by laws of physics must be homogenous. however homogenous equations need not necessarily obey the laws of physics

systematic errors

errors that occur according to some fixed rule or pattern such that measurements yield a consistent over-estimation or under-estimation of the value

random errors

errors of different magnitude and sign such that repeated measurements are scattered about the mean value

accuracy

closeness of a measured value to the true value

precision

closeness of the measured value relative to one another, regardless of the true value

actual/absolute uncertainty

range of values within which the measurement lies

fractional uncertainty

reliability of a chosen instrument to measure a given quantity

distance

total length of the path travelled by a body from the initial position to the final position.

displacement

distance travelled in a straight line in a specified direction from the initial position to the final position.

acceleration

rate of change of velocity

average acceleration

change in velocity over the time taken.

newtons 1st law

a body at rest will stay at rest, and a body in motion will continue to move at constant velocity, unless acted on by a resultant external force.

linear momentum

The linear momentum p of an object of mass m moving with velocity v is defined as the product of its mass and velocity.

p = mv

newtons 2nd law

the rate of change of momentum of a body is directly proportional to the resultant external force acting on it and is in the direction of the resultant force.

F = ma

impulse

the product of the average force and the time interval over which it is applied.

area under the F-t graph

impulse momentum theorem

impulse of the force acting on an object during a time interval is equal to the change in momentum ∆p of the object during that interval.

newtons 3rd law

force exerted by one body on a second body is equal in magnitude and opposite in direction to the force simultaneously exerted by the second body on the first body.

F(AB) = -F(BA)

action reaction pair conditions

• Equal in magnitude

• Opposite in direction

• Acting on different bodies

• Of the same nature (e.g. gravitational, tension, contact)

principle of conservation of momentum

total momentum of the system remains the same provided no resultant external force acts on the system.

perfectly elastic collision

the total kinetic energy of the system is conserved before and after the collision.

(u1 - u2 = v2 - v1)

Relative speed of approach = Relative speed of separation

perfectly inelastic collision

a collision in which the two bodies coalesce (stick together) and move with a common velocity after the collision.

one newton

amount of force required to give a 1 kg mass an acceleration of 1 m s−2

field of force

region of space in which a particle experiences a force due to a physical property that it possesses.

frictional force

when two objects come into physical contact with each other, the component of the contact force parallel to the surface is called the frictional force or friction.

contact force

a force that arises due to two objects coming into physical contact with each other.

normal contact force

component of the contact force perpendicular to the surface

kinetic friction

frictional force which opposes the relative motion between two surfaces in the direction parallel to them.

drag/viscous force

a resistive force which arises when there is relative motion between an object and a fluid

centre of gravity

single point at which the entire weight of the object may be considered to act.

hookes law

the extension or compression x of an elastic object (e.g. spring, wire, rod) is proportional to the applied force F, provided the limit of proportionality is not exceeded.

F = kx

moment of a force about a point

the product of the force and the perpendicular distance from the line of action of the force to the point.

torque of a couple

product of one of the forces and the perpendicular distance between the two forces.

conditions for equilibrium

• the resultant force on the body is zero (i.e. translational equilibrium)

• the resultant torque on the body is zero (i.e. rotational equilibrium).

principle of moments

for a body in rotational equilibrium, the sum of clockwise moments about any point is equal to the sum of anti-clockwise moments about the same point.

work done by constant force

the product of the force and the displacement in the direction of the force.

kinetic energy

energy of a body due to its motion.

potential energy

ability of a body or system to do work due to its position, shape, or state.

conservative force

the work it does on an object moving between two points is independent of the path the object takes.

principle of conservation of energy (POCOE)

Energy can neither be created nor destroyed in any process. It can be transformed from one form to another, and transferred from one body to another, but the total amount remains constant.

power

rate at which work is done

angular displacement

the angle an object makes with respect to a reference line.

one radian

the angle subtended at the centre of circle by an arc equal in length to the radius of the circle.

angular velocity

rate of change of angular displacement.