Download Key Terms - WordPress.com

Speed
How to calculate average speed
How speed cameras are used to measure speed
Calculate speed using a known time and distance
Calculating average speed
Average speed is calculated using this equation:
average speed =
d
total distance
total time
Speed can be measured in different units,
e.g. m/s, km/h, km/s, miles per hour.
s
x
formula triangle
The units of distance and time used will give the units to be used for
speed.
How to calculate average speed
Distance, speed, time, units
t
Speed calculation example
A boy takes 1 hour to travel from his home to the cinema, a
distance of 10 km. Calculate his average speed in km/h.
average speed
(in km/h)
d
=
=
s x t
=
Cover the quantity to be
calculated - s (speed)
How to calculate average speed
Distance, speed, time, units
d (distance in km)
t (time in h)
10 km
1h
10 km/h
Speed calculation example – units check
Sometimes the units have to be changed in a speed calculation. Here is
the same problem but with different units:
A boy takes 1 hour to travel from his home to the cinema, a distance
of 10 km. Calculate his average speed in m/s.
d
d (distance in m)
average speed
=
(in m/s)
t (time in s)
=
s x t
Cover the quantity to be
calculated - s (speed)
10,000 m
3600 s
= 2.8 m/s
How to calculate average speed
Distance, speed, time, units
1x60x60
Question 1
A group set off from home and walk at an average speed
of 3.6 km/h. How far would they travel in two hours?
Give your answer in km.
distance (km) = speed (km/h) x time (h)
d
s
x
= 3.6 km/h x 2 h
t
= 7.2 km
Distance – Time graphs
How to draw and interpret distance-time graphs
That the gradient of a distance-time graph represents speed
Calculate the speed of an object from a graph
Which graph matches which
description?
Libby
James:
Nasir
Mike
Karen
Time
Distance
Gradient =
(speed)
Difference in distance
Difference in time
That the gradient of a distance-time graph represents speed
Distance, speed, time, units
Acceleration and Velocity
How to calculate the acceleration of an object
The difference between speed and velocity
Calculate relative velocity
Recap
1.
Laura covers 2000m in 1,000 seconds. What is her speed?
S = D/T
= 2000m/1000s
= 2 m/s
2. How long would it take to run 100 metres if you run at 10m/s?
T = D/S
= 100m/10m/s
= 10s
3. Steve travels at 50m/s for 20s. How far does he go?
D=SxT
= 50m/s x 20s
= 1000m
Speed vs. Velocity
Speed is simply how fast you are travelling…
This car is travelling at a
speed of 20m/s
Velocity is “speed in a given direction”…
This car is travelling at a
velocity of 20m/s east
The difference between speed and velocity
Speed, velocity, acceleration
Acceleration
Change
in v
Acceleration = change in velocity (in m/s)
(in m/s2)
time taken (in s)
A
E.g:
A Bugatti Veyron can do from 0 – 1609.36m in 25.9 seconds
What is it’s acceleration?
Acceleration =
1609.36 m = 62.14m/s2
25.9 s
How to calculate the acceleration of an object
Speed, velocity, acceleration
T
Force and Motion
the effects force can have on an object
How forces change the motion of objects
Use the equation force=mass x acceleration
Stopping Distances
What a stopping distance is
The affects of stopping distance
Plot graphs to represent stopping distance
Stopping
Distance
The time needed for the driver to react to seeing
something.
Thinking
Distance
The total distance the car travels after the brakes
have been applied
Braking
Distance
The total distance needed to stop a car, including
reaction time.
What a stopping distance is
Stopping, thinking, breaking distance
https://www.youtube.com/watch?v=KGkKDaYd3Mo
What a stopping distance is
Stopping, thinking, breaking distance
Questions
1) What factors can affect the thinking distance?
The factors that can affect thinking distance are; how tired you
are, if you have used drugs or alcohol, distractions including
music, sat navs or other passengers.
2) What factors can affect braking distance?
The factors that can affect braking distance are; the speed of the
car, how good the brakes are and road conditions.
The affects of stopping distance
Stopping, thinking, breaking distance
Work and Power
What the term ‘work done’ means
Work done is the same as energy transferred
Use equations to calculate work and power
Work Done = force x distance
Work
(J)
(N)
(m)
• Work is done when a force moves. People and machines do work.
• When a person lifts a mass or pushes a shopping trolley work is
done.
• The more massive the object lifted or the heavier the shopping in a
trolley, the more work is done because a larger force is being
moved.
• When the object or the trolley is moved a larger distance more work
is done.
What the term ‘work done’ means
Work, power, watt, joules
Power
= work done (J)
Power
(W)
time (s)
• Power is how quickly work is done. If a machine does a lot of work
in a short space of time it has a high power.
• It is measured in joules per second which scientists called watts
(W).
• A large amount of power is measured in kilowatts (kW). 1kW =
1000W
Use equations to calculate work and power
Work, power, watt, joules
Work Done = force x distance
(J)
(N)
(m)
Power = work done (J)
(W)
time (s)
Use equations to calculate work and power
Work, power, watt, joules
Work Done = force x distance
(J)
(N)
(m)
Power = work done (J)
(W)
time (s)
W
F
W
D
P
Use equations to calculate work and power
Work, power, watt, joules
T
Kinetic Energy and Fuelling Vehicles
The factors which affect kinetic energy
How electricity can be used to power vehicles
Discuss the advantges and disadveantages of electric vehicles
Kinetic Energy
Any moving object has energy due to its motion. This is its kinetic energy. Any
moving object has kinetic energy. If an object is not moving, it has zero kinetic
energy.
The size of an object’s kinetic energy depends on the mass of the object
and the speed at which it is travelling.
Kinetic energy = ½ x mass x speed2
(joules, J)
(Kilograms, kg) (metres per second, m/s)2
The factors which affect kinetic energy
Kinetic energy, fuel consumption, fossil fuel
Kinetic Energy
Kinetic energy = ½ x mass x speed2
(joules, J)
(Kilograms, kg) (metres per second, m/s)2
1) Find the kinetic energy of a car of mass 1200kg travelling at 20m/s.
Kinetic energy
= ½ x 1200kg x (20m/s)2
= ½ x 1200 x 400
= 240000J or 240kJ
The factors which affect kinetic energy
Kinetic energy, fuel consumption, fossil fuel
Fuelling Vehicles
Read pages 184 and 185 of your textbook and answer the
following exam questions. (write the question and answer)
1) Explain what it means when we say that electric cars don’t
produce pollution at their point of use. (2 marks)
2) State and explain 3 factors which affect fuel consumption of
a typical car. (3 marks)
3) Outline the advantages and disadvantages of using electric
cars over conventional fossil fuel powered cars. (6 marks
QWC)
https://www.youtube.com/watch?v=s0seCNxRUmI
How electricity can be used to power vehicles
Kinetic energy, fuel consumption, fossil fuel
Extended writing question
Outline in detail two advantages and two disadvantages of using biofuels to
generate electricity.
1) How will you structure your answer?
2) What is the question asking you?
3) What keywords should you include?
Describe the advantages and disadvantages of using fossil fuels and
biomass
Biofuel, biomass, fossil fuel
Collisions and Car Safety
The safety features of cars
The effectiveness of safety features
Calculate momentum
Safety Features
Paddle
control
seatbelt
airbag
Crumple
zone
Electric
windows
Collapsible
steering
column
ABS
The safety features of cars
Momentum, crumple zone, ABS
Traction
control
Momentum
• During a collision a quantity
called momentum is conserved.
When the car slows down during
impact its momentum decreases.
As it decreases, the passengers
feel a force which can result in
injury, e.g. whiplash.
• The force experienced by a
passenger during a collision
depends upon the rate of
changes of momentum. The
quicker the change in
momentum, the greater the force
experienced.
• You can calculate momentum
using this equation:
• You can calculate the force using
the following equation:
momentum = mass x velocity
Force (N) = change in momentum (kg m/s)
time taken (s)
The safety features of cars
Calculate momentum
6 Mark Question
The safety features of cars
Calculate momentum
Falling objects and drag
How to calculate the weight of an object
The motion of an object falling under gravity
Explain that drag increases with speed
Terminal Speed
• When a skydiver jumps out of an aeroplane, the speed of their descent
can be considered in two separate parts:
• Before the parachute opens (when the skydiver is in free-fall).
• After the parachute opens (when air resistance is greatly increased).
The motion of an object falling under gravity
Weight, gravitational field strength, drag
Weight and Mass
• Weight is due to the force of gravity of an object.
• The mass of an object is the amount of matter that it contains. Weight and
mass are linked by two related formulae:
Weight (N) = Mass (kg) x Acceleration or free-fall (m/s²) or Gravitational field
strength (N/kg)
How to calculate the weight of an object
Weight, gravitational field strength, drag
Gravity
• Gravitational field strength or acceleration due to gravity:
 is unaffected by atmospheric changes
 varies slightly at different points on the Earth’s surface
 will be slightly different on the top of a mountain or down a
mineshaft.
Gravitational potential energy
What factors affect GPE
The energy changes taking place as an object falls
Calculate GPE using an equation
The Conservation of Energy
• Energy cannot be created or destroyed. It is converted into
different forms.
• For a roller coaster, energy is transformed between gravitational
potential and kinetic energy.
• The principle of conservation of energy tells us that
gravitational potential energy (GPE) at the top of a roller coaster
= kinetic energy (KE) at the bottom + energy transferred as heat
and sound.
Gravitational Potential Energy
• The gravitational potential energy (GPE) of an object is the energy stored
due to:
 its position in the Earth’s gravitational field (height)
 its mass.
• You can calculate GPE using this formula:
mass x gravitational field strength x vertical height
(kg)
(N/kg)
(m)
Fairground Rides
• At the peaks on the ride the train has a lot of
GPE (high up) and little KE (moves slowly).
• In the middle of the ride GPE is decreasing and
KE is increasing.
• The more GPE gained by the train on the roller
coaster, the greater it’s maximum speed.
• At the bottom the train has little GPE (low
down) but a lot of KE (moves fast).