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Contact force
A push or pull on one object by another that is touching it
Displacement
A vector quantity. Distance and direction of an object's change in position from the starting point.
newtons (N)
The unit of force
Non-contact force
a force that one object can apply to another object without touching it
Scalar
a physical quantity that has magnitude but no direction
Vector
A physical quantity that has magnitude and direction
Velocity
A vector quantity. The speed of an object in a given direction
Average speed
total distance divided by total time
Distance-time graph
A graph with distance on the vertical axis and time on the horizontal axis
Gradient
The slope of a line on a graph
Speed
Distance/time
Tangent
A straight line or plane that touches a curve or curved surface at one point.
Acceleration
Change in velocity
Air resistance
Fluid friction acting on an object moving through the air
Deceleration
negative acceleration
Velocity-time graph
A graph with time on the x axis and velocity on the y axis.
Uniform motion
Motion at a constant speed in a straight line
Gravitational field strength
The strength of a gravitational field. On the earth's surface g = 9.8 N/kg.
Mass
the amount of matter in an object
Weight
A measure of the force of gravity on an object
Balanced forces
forces acting on an object that combine and form a net force of zero
Equilibrium
a state of balance between opposing forces
Newton's first law
when the resultant force is zero, the acceleration must be zero
Resultant force
The resultant of a system of force is the vector sum of all forces.
Unbalanced forces
Forces acting on an object that combine and form a resultant force that is not zero
Inertia
The tendency of an object to resist any change in its motion.
Newton's second law
force is acceleration times mass (F=ma)
Newton's third law
for every action there is an equal and opposite reaction
Momentum
Mass x Velocity
Conservation of momentum
The total momentum of a system remains unchanged after a collision or interaction.
Crumple zones
Crumple on impact, increasing the time taking for the car to stop
Braking distance
the distance your car travels after you apply the brakes
Reaction time
the amount of time taken to respond to a specific stimulus
Stopping distance
thinking distance + braking distance
Thinking distance
The distance travelled during the driver's reaction time
Centre of mass
The point in an object where the mass of an object seems to act.
Moment
the turning effect of a force
Pivot
Point upon which an object turns or rotates
Newton-metre (Nm)
The unit of moments
Gear
A device that transmits rotational force against another gear or device.
Lever
a simple machine that consists of a bar that pivots at a fixed point called a fulcrum
Density
Mass per unit volume
pascal (Pa)
The unit of pressure
Pressure
Force per unit area.
Upthrust
The upward force that liquids and gases exert on objects.
Atmospheric pressure
The pressure caused by the weight of the atmosphere
Compression
A force that pushes on or squeezes a material.
Elastic deformation
Caused when a material is compressed, bent, or stretched, and can return to its original shape
Elastic potential energy
Energy stored by something that can stretch or compress
Extension
The change in length of an object
Inelastic deformation
occurs when an object has been stretched or compressed so much that it cannot return to its original shape
Limit of proportionality
The point at which materials stop obeying Hooke's Law
Spring constant
The constant of proportionality in Hooke's Law
scalar quantity
quantity defined by numbers only - eg speed
vector quantity
quantity defined by speed AND direction eg velocity
resultant
the overall force acting on an object
force
A push, pull that can change the direction or speed of an object. Measured in Newtons (N)
weight
The force acting on an object by gravity
gravity
creates a pull acting on a mass.
push, pull, change direction, change shape
The things a force can do to an object
air resistance
A force that slow things down that are moving through air. It is a type of friction.
contact force
A force that needs to touch an object before it can affect it (e.g. friction).
drag
Air resistance and water resistance are both sometimes called drag.
force meter
Piece of equipment containing a spring, used to measure forces in Newtons (N).
friction
A force that can slow things down when two things rub against each other. Friction generates heat.
magnetism
A force that attracts objects made out of iron.
newton (N)
The unit of force.
newton meter
Another name for a force meter.
non-contact force
A force that can affect something from a distance (e.g. gravity).
speed
How fast something is moving. Often measured in metres per second (ms⁻¹).
static electricity
A force which attracts things with opposite electrical charges on them.
upthrust
A force that pushes things up in fluids.
water resistance
A force that tries to slow things down that are moving through water. It is a type of friction.
density
The amount of mass that 1cm³ of a substance has. Measured in g/cm³.
displacement
How far out of place an object is
F=ma
Force = mass x acceleration.
Work done =
Force x distance
Factors affecting thinking distance
Drugs, alcohol, tiredness
Factors affecting braking distance
Road condition, tyre condition, weather
Stopping distance =
Thinking + braking distance
