Speed

Distance per unit time

Distance

Length between 2 distinct points

Velocity

Displacement per unit time

Displacement

Distance travelled in a particular direction from a reference point

Acceleration

Change in velocity per unit time

Vector

Quantity that has both magnitude and a given direction

Scalar

Quantity that has only magnitude

Examples of vector quantities

Momentum

Examples of scalar quantities

Energy

Temperature

Value of g

g = 9.81

Speed equation

Speed = distance / time

Velocity equation

Velocity = displacement / time

Gradient of displacement-time graph

Area beneath velocity-time graph

Equations of constant acceleration

v = u + at

v² = u² + 2as

s = ut + ½at²

s = ½(u+v)t

Projectiles have…

Horizontal and vertical components of motion

Equation for stopping distance

Stopping distance = thinking distance + braking distance

Thinking distance

Distance the car travels between the driver seeing the hazard and applying the brakes

Braking distance

Distance the car travels between the driver applying the brakes and the car coming to rest

Thinking distance equation

thinking distance = speed of car * reaction time of driver

Braking distance equation

d = (1/2mv^2) / F

factors that increase thinking distance

tiredness

alcohol + drugs

distractions

age of driver

factors that increase braking distance

higher speed

poor road conditions

poor condition of tyres

mass of car

equation for net force

f = ma

resultant force

single force which has the same effect as the sum of all the forces acting on a body

newton

the force that casues a mass of 1 kg to have an acceleration of 1 ms^-2

weight equation

w = mg

tension

the force in a string or cable when stretched

normal contact force (reaction force)

the force that acts perpendicular to the point of contact of the body and the surface

upthrust

upwards force that a fluid exerts on a body floating in it due to the fluid being displaced

friction

the force between 2 surfaces in contact with each other

drag

the frictional force experienced by an object travelling through a fluid

factors affecting drag

cross-sectional area of object

density of fluid

terminal velocity

object initially accelerates as the downwards gravitational force is greater than the resistive forces

drag on the object increases as it accelerates

eventually drag = weight of object

resultant force = 0

falls at a constant velocity (terminal velocity)

equilibrium

resultant force acting on an object = 0

turning moment (moment of force)

the turning effect of a force around a fixed point

the product of a force and the perpendicular distance of its line of action from the point

couple

when 2 equal, antiparallel forces act to produce a rotation

torque

turning effect of a couple

principle of moments

states that for an object in rotational equilibrium, the sum of anticlockwise moments equals the sum of clockwise moments

centre of mass

the single point at which all of the mass of the object can be assumed to be situated

(for a symmetrical body of constant density, the centre of mass will be at the centre of the object)

centre of gravity

the single point through which the entire weight of the object can be thought to act

experiment to determine centre of mass / gravity of an object

make 3 holes in random places on the edge of the shape

hang shape from first hole

let shape swing and come to rest

use plumb line to draw a vertical line down from the point of suspension to the bottom of the shape

repeat steps from a different hole

there will now be 2 lines on the shape, where they cross is the centre of mass / gravity of the shape

define density

mass per unit volume

density equation

density = mass / volume

archimedes principle

states that the upthrust exerted on an object is equal to the weight of the fluid displaced by the object

define pressure

force per unit area

pressure equation

pressure = force / area

equation for pressure exerted by a fluid

p = hpg

what happens with pressure as you descend further underwater?

pressure increases with depth in water because of the force exerted by the increased weight of the water above

for equilibrium of an object in a fluid…

upthrust = weight downwards

equation for upthrust

upthrust = Ahpg

joule

energy transferred when a force of 1 newton causes an object to move a distance of 1 metre in the direction of the force

equation for work done

w = fd

work done = energy transferred

.

equation for work done by a force at an angle

w = Fcosθ

conservation of energy

energy cannot be created or destroyed, it can only be transferred from one form to another

gravitational potential energy

energy an object has due to its position in a gravitational field

E = mgh

kinetic energy

energy an object has due to its speed

E = 1/2mv^2

kinetic energy of an object depends on 2 factors:

mass

velocity

exchange between gravitational potential energy and kinetic energy

loss in GPE = gain in kinetic energy

power

rate of energy transfer

watt

joules transferred per second

equations for power

P = Fv

P = wd / t

define efficiency

the ratio of useful energy output to total energy input

efficiency equation

efficiency = useful energy output / total energy input

define elastic deformation

the object will return to its original shape when the deforming force is removed

define plastic (inelastic) deformation

the object won’t return to its original shape when the deforming force is removed

define tensile force

2 equal and opposite forces acting on a wire in order to stretch it

extension

define compressive force

2 or more forces that have the effect of reducing the volume of the object on which they are acting, or reducing the length of a spring

compression

hooke’s law

the extension of an object is proportional to the force that causes it, provided that the elastic limit is not exceeded

equation for hooke’s law

F = kx

what does the area under the graph of a force-extension graph represent?

work done

equations for elastic potential energy

E = 1/2Fx

E = 1/2kx^2

define tensile stress

force per unit cross-sectional area

define tensile strain

extension per unit length

define ultimate tensile strength

the maximum stress a material can withstand while being pulled or stretched, before it fails or breaks

define young modulus

the ratio between stress and strain

equation for young modulus

young modulus = stress / strain

stress-strain graph for brittle material

stress-strain graph for ductile material

stress-strain graph for polymeric material

newton’s first law

a body will remain at rest or continue to move at a constant velocity unless acted on by an external force

newton’s second law

the resultant force on an object is proportional to the rate of change of momentum of the object, and the momentum change takes place in the direction of the force

newton’s third law

if object A exerts a force on object B, then object B will exert an equal and opposite force on object A

newton’s second law equation

F = ma

momentum equation

p = mv

3 key things to remember about momentum

momentum is a vector quantity - it has both magnitude and direction

momentum is directly proportional to both mass and velocity - doubling either means that the momentum will also double

momentum is conserved in any collision or interaction

the principle of conservation of momentum

the total momentum before a collision equals the total momentum after the collision, provided that no external forces are involved

define impulse

the product of a force and the time for which the force acts

impulse equation

impulse = force * change in time

net force =

rate of change of momentum

equation for net force (rate of change of momentum)

F = change in momentum / change in time

area under a force-time graph =

impulse

define elastic collision

collision in which the momentum and the kinetic energy are conserved

define inelastic collision

collision in which the momentum is conserved but some of the kinetic energy is transferred to other forms in the collision

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