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Distance-time graphs
• A distance-time graph shows the distance
an object moves in period of time.
• To work out the speed of the object from
you graph you look at the gradient and do:
• speed = change in distance/change in
time
• The steeper the gradient, the faster the
object is moving.
• If the graph is curved, this shows speed
changing gradually.
Velocity, acceleration &
direction.
• The velocity of an object is its speed in a
given direction.
• A change in velocity (speeding up or slowing
down) is called acceleration or
deceleration.
• The calculation for working out
acceleration is
• acceleration = change in velocity/ time
taken for change
Velocity-time graphs.
• A velocity-time graph shows how the
velocity of an object changes with time.
• The gradient of a velocity-time graph
represents acceleration.
• The area under the line shows distance
travelled.
Terminal velocity.
• An object falling through the air
eventually reaches a top speed, its
terminal velocity.
• At this speed, the force of weight
downwards balances the force of air
upwards.
• At this point the resultant force is 0.
Forces.
• For every force, there is an equal and
opposite force.
• Balanced forces have the same value
but act in opposite directions.
• An object will remain stationary or
move at a constant speed unless an
external force acts upon it.
To calculate force:
• Force = Mass x Acceleration
• The smaller the mass, the bigger the
acceleration.
• The bigger the force, the bigger the
acceleration.
Stopping distance.
• If a driver has to stop suddenly, the
stopping distance depends on the distance
the car travels during the driver’s reaction
time (thinking distance) and then while the
brakes are applied (braking distance).
• stopping distance = thinking distance x
braking distance
• thinking distance = speed x reaction time
• The greater the speed, the greater the
stopping distance.
Work, energy and force.
• The work done is the energy required
to move an object.
• The equation for this is:
work done (J) = force (N) x distance
moved (m)
Transferring &
transforming energy.
• Kinetic energy is the energy of movement.
• The kinetic energy of an object increases
when its mass/speed increases.
• The kinetic energy of an object decreases
when its mass/speed decreases.
• If an object hits another object and stops,
the kinetic energy is transferred, but if
the object does not quite stop, then only
some of the energy is transferred.
• In an experiment using a car rolling down a
ramp, the car would have potential energy
at the top of the ramp which would then
be transformed into kinetic energy as it
started to move.
The equation for calculation kinetic energy is:
kinetic energy = 1/2mv (mass, velocity)
The equation for calculating potential energy
is:
potential energy = mgh (mass x gravity x
height)
Momentum.
• Objects have momentum when they move.
• The calculation for working out momentum
is:
• momentum = mass x velocity
• Momentum is not the same as kinetic
energy because momentum is a vector
quantity meaning it has a direction as well
as a size but kinetic energy is a scalar
quantity meaning it only has a size.
• A force can change an objects
momentum by changing its velocity:
• change in momentum = mass x
change in velocity
• A force can also change an objects
momentum by changing its direction.
• A change in momentum depends on
the size of the force and the time
over which it acts. The force is given
by:
• force = change in momentum/time
Static electricity.
• When two materials are rubbed
together, negatively charged electrons are
transferred from one to the other making
both materials electrically charged.
• If an object gains electrons, it has
a negative charge and if it loses electrons
it has a positive charge.
• Their charges are equal and opposite static
electrical charges.
• Like charges repel, unlike charges
attract.
• Insulators (e.g.. plastic, glass) hold
electrical charge.
• Electrical conductors (e.g.. metals,
water) allow charge to flow as an
electrical current in a closed circuit.
• Static electricity can be dangerous if
sparks cause flammable materials to
ignite or explode. Earthing prevents a
build up of static charge.