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# Physics Defintions

### AS Physics definitions

Define Newton Unit of force. The force that causes an object of mass 1kg to accelerate at 1m/s^2.
Define Weight the force on the object due to gravity.
Define Scaler A physical quantity with magnitude (size), but not direction, e.g. speed, distance, pressure, potential difference, density and energy.
Define Vector A physical quantity with magnitude (size) and a direction, e.g. velocity, acceleration and force.
Define displacement The distance travelled in a particular direction. Therefore a vector.
Instantaneous speed The speed of an object given at a certain moment in time.
Define average speed Measure of the total distance travelled in a unit of time.
Define velocity Displacement divided by time.
Define acceleration The rate of change of velocity.
Define terminal velocity The velocity at which an objects drag is equal to its accelerating force. Therefore there is no resultant force and zero acceleration.
Define Newtons Second Law Net Force = mass x acceleration.
Define drag The resistive force that acts on a body when it moves through a fluid.
Equilibrium When the net force or resultant force is equal to zero.
Define centre of gravity The point where the entire weight of an object appears to act.
Define couple A pair of forces equal to each other that tend to produce a rotation only.
Define torque of a couple The turning affect due to a couple.
Define moment of a force The turning effect due to a single force, calculated from the force x the perendicular distance from a given point.
Define thinking distance The distance travelled from seeing the need to stop (hazard) to applying the brakes.
Define braking distance The distance travelled by a vehicle whilst decelerating to a stop.
Define stopping distance The distance a vehicle travels while decelerating to a stop. The sum of the thinking distance and the braking distance.
Define work done The force x distance moved in the direction of the force.
Define joule Unit of energy. 1J is the work done when a force of 1N moves an object 1m in the direction of the force.
Define conservation of energy States that no energy can be created or destroyed, only converted from one form into another.
Define power The rate of work done.
Define the watt The unit of power. 1W is 1J of energy transferred per second.
Define efficiency The ratio of useful output energy to total input energy. Useful output divided by total input x 100(%).
Define tensile force Usually two equal and opposite forces acting on a wire in order to stretch it.
Define compressive force Two or more forces that have the effect of reducing the volume of the object on which they are acting or reducing the length.
Define extension The change in length of an object when subjected to a tension.
Define elastic limit The point at which elastic deformation becomes pastic deformation.
Define elastic deformation The object will return to its original shape when the deforming force is removed.
Define plastic deformation The object will not return to its original shape when the deforming force is removed. It becomes permenantly deformed.
Define ductile material Materials that have a large plastic region and can therefore be drawn into a wire, e.g. copper.
Define brittle material A material that distorts very little, even when subject to a large stress and does not exhibit any plastic deformation, e.g. concrete.
Define limit of proportionality The point at which an object no longer obeys Hookes Law.
Define Hookes Law The extension of an elastic body is proportional to the force that causes it up to the limit of proportionality.
Define the force constant The force per unit extension or compression.
Define elastic potential energy The energy stored in a stretched or compressed object, e.g. a spring.
Define stress The force per cross-sectional area.
Define strain The extension per unit length.
Define Young's Modulus The ratio between stress and strain. Stress divided by strain.
Define ultimate tensile strength The maximum tensile force that can be applied to an object before it breaks.
Created by: physicsdavid