Distance-time graphs 40 30 20 10 0 20 40 60 80100 4) Diagonal line downwards = 3) Steeper diagonal line = 1)Diagonal line = 2) Horizontal line = Distance

Distance-time graphsDistance-time graphs

40

30

20

10

0 20 40 60 80 100

4) Diagonal line

downwards =

3) Steeper diagonal line =1) Diagonal line =

2) Horizontal line =

Distance

(metres)

Time/s

© George Spencer School 2010

40

30

20

10

0 20 40 60 80 100

1) What is the speed during the first 20 seconds?

2) How far is the object from the start after 60 seconds?

3) What is the speed during the last 40 seconds?

4) When was the object travelling the fastest?

Distance

(metres)

Time/s



Distance-time graph for non-uniform motionDistance-time graph for non-uniform motion

40

30

20

10

0 20 40 60 80 100

Distance

(metres)

Time/s

Object is accelerating up to here

Object is now

decelerating



AccelerationAcceleration V-U

TA

Acceleration = change in speed (in m/s)

(in m/s2) time taken (in s)

1) A cyclist accelerates from 0 to 10m/s in 5 seconds. What is her acceleration?

2) A ball is dropped and accelerates downwards at a rate of 10m/s2 for 12 seconds. How much will the ball’s speed increase by?

3) A car accelerates from 10 to 20m/s with an acceleration of 2m/s2. How long did this take?

4) A rocket accelerates from 1,000m/s to 5,000m/s in 2 seconds. What is its acceleration?



Speed-time graphsSpeed-time graphs

80

60

40

20

0 10 20 30 40 50

Velocity

m/s

T/s

1) Upwards line =

2) Horizontal line =

3) Upwards line =

4) Downward line =



80

60

40

20

0

1) How fast was the object going after 10 seconds?

2) What is the acceleration from 20 to 30 seconds?

3) What was the deceleration from 30 to 50s?

4) How far did the object travel altogether?

10 20 30 40 50

Velocity

m/s

T/s



Speed-time graph for non-uniform motionSpeed-time graph for non-uniform motion

40

30

20

10

0 20 40 60 80 100

Distance

(metres)

Time/s

Object’s acceleration is increasing

Object’s acceleration is decreasing



Introduction to ForcesIntroduction to ForcesA force is a “push” or a “pull”. Some common examples:

Weight (mg) – pulls things towards the centre of the Earth

Air resistance/drag – a contact force that acts against anything moving through air or liquid

Upthrust – keeps things afloat

_____ – a contact force that acts against anything moving



Balanced and unbalanced Balanced and unbalanced forcesforces

Consider a camel standing on a road. What forces are acting on it?

Weight

Reaction

These two forces would be equal – we say that they are BALANCED. The camel doesn’t move anywhere.




What would happen if we took the road away?

Weight

Reaction

The camel’s weight is no longer balanced by anything, so the camel falls downwards…



Air ResistanceAir ResistanceAir resistance is a force that opposes motion through air. The quicker you travel, the bigger the air resistance:

The same applies to a body falling through a liquid (called “drag” or “upthrust”).



Examples of Air ResistanceExamples of Air Resistance







1) This animal is either ________ or moving with _____ _____…

4) This animal is…

2) This animal is getting _________…

3) This animal is getting _______….



Force and accelerationForce and acceleration

If the forces acting on an object are unbalanced then the object will accelerate, like these wrestlers:

Force (in N) = Mass (in kg) x Acceleration (in m/s2)

F

AM© George Spencer School 2010


Force, mass and accelerationForce, mass and acceleration

1) A force of 1000N is applied to push a mass of 500kg. How quickly does it accelerate?

2) A force of 3000N acts on a car to make it accelerate by 1.5m/s2. How heavy is the car?

3) A car accelerates at a rate of 5m/s2. If it weighs 500kg how much driving force is the engine applying?

4) A force of 10N is applied by a boy while lifting a 20kg mass. How much does it accelerate by?

F

AM



Stopping a car…Stopping a car…

Braking distance

Too much alcoholThinking

distance

(reaction time)

Tiredness

Too many drugs

Wet roads

Driving too fast

Tyres/brakes worn out

Icy roads

Poor visibility



Car Safety FeaturesCar Safety Features



Work doneWork done

When any object is moved around work will need to be done on it to get it to move (obviously).

We can work out the amount of work done in moving an object using the formula:

Work done = Force x distance moved

in J in N in m

W

DF© George Spencer School 2010


Example questionsExample questions1. Bori pushes a book 5m along the table with a force of

5N. He gets tired and decides to call it a day. How much work did he do?

2. Alicia lifts a laptop 2m into the air with a force of 10N. How much work does she do?

3. Martin does 200J of work by pushing a wheelbarrow with a force of 50N. How far did he push it?

4. Chris cuddles his cat and lifts it 1.5m in the air. If he did 75J of work how much force did he use?

5. Carl drives his car 1000m. If the engine was producing a driving force of 2000N how much work did the car do?



Work and PowerWork and PowerThe POWER RATING of an appliance is simply how much work it does (i.e. how much energy it transfers) every second.

In other words, 1 Watt = 1 Joule per second

W

TP

W = Work done (in joules)

P = Power (in watts)

T = Time (in seconds)



Some example questionsSome example questions1) What is the power rating of a light bulb that transfers

120 joules of energy in 2 seconds?

2) What is the power of an electric fire that transfers 10,000J of energy in 5 seconds?

3) Isobel runs up the stairs in 5 seconds. If she transfers 1,000,000J of energy in this time what is his power rating?

4) How much energy does a 150W light bulb transfer in a) one second, b) one minute?

5) Simon’s brain needs energy supplied to it at a rate of 40W. How much energy does it need during a physics lesson?

6) Ollie’s brain, being more intelligent, only needs energy at a rate of about 20W. How much energy would his brain use in a normal day?



Kinetic energyKinetic energyAny object that moves will have kinetic energy.

The amount of kinetic energy an object has can be found using the formula:

Kinetic energy = ½ x mass x velocity squared

in J in kg in m/s

KE = ½ mv2



Example questionsExample questions

1) Nicole drives her car at a speed of 30m/s. If the combined mass of her and the car is 1000kg what is her kinetic energy?

2) Shanie rides her bike at a speed of 10m/s. If the combined mass of Shanie and her bike is 80kg what is her kinetic energy?

3) Dan is running and has a kinetic energy of 750J. If his mass is 60kg how fast is he running?

4) George is walking to town. If he has a kinetic energy of 150J and he’s walking at a pace of 2m/s what is his mass?



Terminal SpeedTerminal SpeedConsider a skydiver:

1) At the start of his jump the air resistance is _______ so he _______ downwards.

2) As his speed increases his air resistance will _______

3) Eventually the air resistance will be big enough to _______ the skydiver’s weight. At this point the forces are balanced so his speed becomes ________ - this is called TERMINAL SPEED

Words – increase, small, constant, balance,

accelerates© George Spencer School 2010


Terminal SpeedTerminal Speed

Consider a skydiver:

4) When he opens his parachute the air resistance suddenly ________, causing him to start _____ ____.

5) Because he is slowing down his air resistance will _______ again until it balances his _________. The skydiver has now reached a new, lower ________ _______.

Words – slowing down, decrease, increases, terminal

speed, weight© George Spencer School 2010


Velocity-time graph for terminal Velocity-time graph for terminal velocity…velocity…

Velocity

Time

Speed increases…

Terminal velocity reached…

Parachute opens – diver slows down

New, lower terminal velocity reached

Diver hits the ground

On the Moon



Gravitational Potential Gravitational Potential EnergyEnergy

To work out how much gravitational potential energy (GPE) an object gains when it is lifted up we would use the simple equation…

GPE = Mass x Acceleration of free-fall x Change in height

(Joules) (newtons) (=10N/kg) (metres)



Some example questions…Some example questions…

How much gravitational potential energy have the following objects gained?:

1. A brick that has a mass of 1kg lifted to the top of a house (10m),

2. A 1,000kg car lifted by a ramp up to a height of 2m,

3. A 70kg person lifted up 50m by a ski lift.

How much GPE have the following objects lost?:

1. A 200g football dropping out of the air after being kicked up 30m,

2. A 500gN egg falling 10m out of a bird nest,

3. A 1,000kg car falling off its 2m ramp.

4. Nathan when falling 1.5m to the ground after being hit by a van (Nathan’s mass is around 80kg).© George Spencer School 2010


Roller CoastersRoller Coasters1) Electrical energy is transferred into gravitational potential energy

2) Gravitational potential energy is transferred into kinetic energy

3) Kinetic energy is transferred back into gravitational potential energy



Weight vs. MassWeight vs. MassEarth’s Gravitational Field Strength is 10N/kg. In other

words, a 1kg mass is pulled downwards by a force of 10N.

W

gM

Weight = Mass x Gravitational Field Strength

(in N) (in kg) (in N/kg)

1) What is the weight on Earth of a book with mass 2kg?

2) What is the weight on Earth of an apple with mass 100g?

3) Dave weighs 700N. What is his mass?

4) On the moon the gravitational field strength is 1.6N/kg. What will Dave weigh if he stands on the moon?



Documents

Distance-time graphs 40 30 20 10 0 20 40 60 80100 4) Diagonal line downwards = 3) Steeper diagonal line = 1)Diagonal line = 2) Horizontal line = Distance