Section 1: Motion, Forces & Conservation of Energy Flashcards
What is a scalar quantity?
A quantity that only has a magnitude but no direction
What is a vector quantity?
A quantity that has a magnitude and a direction
What are examples of scalar quantities?
Speed
Mass
Distance
Energy
What are examples of vector quantities?
Velocity
Displacement
Weight
Force
Acceleration
Momentum
What is distance?
How far an object has moved (not including its direction)
SCALAR
What is displacement?
The distance and direction in a straight line from an objects starting point to its finishing point
VECTOR
What is speed?
How fast your going with no regard to direction
SCALAR
What is velocity?
Speed in a certain direction
VECTOR
What is acceleration?
The change in velocity in a certain amount of time
What is the acceleration of an object due to gravity close to Earths surface?
10m/s^2
What is the typical speed (m/s) of walking?
1.4 m/s
What is the typical speed (m/s) of running?
3 m/s
What is the typical speed (m/s) of cycling?
5.5 m/s
What is the typical speed (m/s) of a car in a built up area?
13 m/s
What is the typical speed (m/s) of a car on a motorway?
31 m/s
What is the typical speed (m/s) of a train?
Up to 55 m/s
What is the typical speed (m/s) of a plane?
250 m/s
What is the typical speed (m/s) of wind?
5 - 20 m/s
What is the typical speed (m/s) of sound?
340 m/s
What does a flat line show on a distance time graph?
The object is stationary
What does a steepening curve show on a distance time graph?
Object is accelerating
What does a straight line show on a velocity time graph?
Object is travelling at a steady speed
What does a curve that’s levelling off show on a distance time graph?
Deceleration
What is deceleration?
Negative acceleration - shows an object is slowing down
What does a gradient show on a distance time graph?
Speed
How to calculate gradient?
Rise/run
What does a flat line show on a velocity time graph?
The object is travelling at a steady speed
What does an uphill straight line show on a velocity time graph?
There is a constant acceleration
What does a steepening curve show on a velocity time graph?
Increasing acceleration
What does a downhill straight line show on a velocity time graph?
A constant deceleration
What does a gradient show on a velocity time graph?
Acceleration
What does the area under the graph show on a velocity time graph?
Distance travelled in that given time
What is Newton’s first law?
An object remains in the same state of motion unless a resultant force acts on it. If the resultant force on an object is zero, this means:
a stationary object stays stationary
a moving object continues to move at the same velocity (at the same speed and in the same direction)
What is Newton’s second law?
Force = mass x acceleration
What is Newton’s third law?
If object A exerts a force on object B, object B will exert the same force in the opposite direction onto object A
What happens when a girl pushes on a wall (relate to Newton’s third law)?
The wall will push back on the girl with equal and opposite force
What is weight?
The force due to gravity
What is weight caused by near Earth?
The gravitational field around Earth
What does object weight depend on?
Strength of gravitational field at the objects location
What is inertial mass?
The measure of how hard it is to change an objects velocity due to its mass
It’s the ratio of force over acceleration: mass = force/acceleration
What happens to velocity when an object travels in a circular motion with constant speed?
Has a constantly changing velocity BECAUSE direction constantly changes too
What does a changing velocity mean?
The object is accelerating so there’s a resultant force acting on it
What is the force called that’s produced by a circular motion?
Centripetal force - acts towards the centre of the circle
What is the correlation between the mass and momentum of an object?
The greater an objects mass, the greater its momentum
What is the correlation between the velocity and momentum of an object?
The greater an objects velocity, the greater its momentum
What is conservation of momentum?
In a closed system, total momentum before an event equals total momentum after an event
How can Newton’s third law be linked with momentum (use example of two balls)?
- Ball A collides with ball B
- Ball A and ball B exert equal and opposite forces on eachother due to Newton’s third law
- Due to f=ma, ball A decelerates at the same rate that ball B accelerates
- The time the force is applied is the same for both balls, so their change in speed is the same
- Momentum is lost by ball A equals momentum gained by ball B. So total momentum before equals total momentum after
What is the typical human reaction time?
0.2 - 0.9 s
What are the three factors that affect reaction time?
Tiredness
Drugs and alcohol
Distractions
What is the process of doing the ruler test?
- Get someone to hold a ruler so zero is between your thumb and forefinger
- Ruler is dropped without warning and catch it as quickly as possible whilst a stopwatch is pressed and stoped when the ruler is caught
- Use the distance that the ruler fell to calculate the reaction time
What is the stopping distance equation?
Stopping distance = thinking distance + braking distance
What are the 2 factors that increase thinking distance?
Faster vehicle speed
Longer driver reaction times
What are the 4 factors that increase braking distance?
Faster vehicle speed
Heavier vehicle
Poor, wet or icy road surface
Damaged or worn brakes or tyres
What is thinking distance?
How far the vehicle moves during the drivers reaction time
What is braking distance?
The distance taken to stop whilst brakes are applied
What happens to thinking distance and braking distance if speed doubles?
Thinking distance doubles
Braking distance quadruples
What happens for a car to stop?
When: work done by brakes = energy in cars kinetic energy store
What is a good estimated for a cars mass?
1000kg
How does a larger braking force impact deceleration? Why?
Larger breaking force means a larger deceleration BECAUSE…
the faster a vehicle is going, the greater the braking force needed to make it stop in a certain distance
What can large decelerations do to cars and the road?
Cars: can cause brakes to overheat
Roads: can cause vehicle to skid - DANGEROUS
What are the 8 types of energy store?
Kinetic
Gravitational potential
Elastic potential
Electrostatic
Thermal
Chemical
Magnetic
Nuclear
What are the 4 types of energy transfer?
Mechanical (a force doing work)
Electrical (work done by moving charges)
Heating
Radiation (e.g. light or sound)
What is a system?
A single object or a group of objects
What is conservation of energy?
Idea that energy can be transferred usefully, can be stored or dissipated BUT CANNOT be created or destroyed
What is a closed system?
When no energy (or matter) is transferred in or out of the system, so there is not net change in total energy
What are the energy transfers for an arm throwing a ball up?
Chemical energy store of the arm —> kinetic energy store of ball and arm
BECAUSE WORK DONE MECHANICALLY BY FORCE EXERTED BY ARM
What are the energy transfers for a ball falling?
Gravitation potential energy store of ball —> kinetic energy store of the ball
BECAUSE WORK DONE MECHANICALLY BY GRAVITATIONAL FORCE
What are the energy transfers for a kettle boiling water?
Mains —> thermal energy store of kettles heating element —> thermal energy store of water
BECAUSE ENERGY WAS TRANSFERRED ELECTRICALLY FIRST THEN TRANSFERRED BY HEAT
What is the equation for efficiency?
Useful energy transferred/total energy supplied
Why is no device 100% efficient?
In all systems, energy is wasted to a store thats not useful (usually thermal)
What does the width of the arrow show in a Sankey diagram?
The energy supplied
Steps to drawing a Sankey diagram?
- Create a key
- First relate the TOTAL energy supplied to the key and draw that width
- Coming horizontally from the total energy line, draw an arrow the size of the USEFUL energy that’s related to the key
- Coming vertically from just after the total energy line and just before the useful energy arrow, draw an arrow the size of the WASTED energy that’s related to the key
How does lubrication work (process)?
- The frictional force acts between moving gears, so energy is wasted and dissipated in an unwanted energy transfer
- Apply lubricant
- Frictional force is reduced so less energy is wasted
What does thermal insulation do? How?
Reduces unwanted energy transfers by heating an object
E.g. using cotton wool
What do lubrication and thermal insulation essentially do to efficiency?
Increase efficiency of useful energy transfers
What are the two ways to decrease how quickly a building cools?
- Increase thickness of its walls
- Make walls out of material with lower thermal conductivity
What is conduction?
Where vibrating particles transfer energy to neighbouring particles
What is the correlation between a materials thermal conductivity and the rate at which energy transfers by conduction?
The higher a materials thermal conductivity, the faster it transfers energy by conduction
What are the ways to reduce energy loss?
Lubricaiton
Thermal insulation
Double glazed windows
What is a non renewable energy resource?
Energy resources that will run out one day
What is a renewable energy resource?
Energy resources that will never run out
What are the 3 examples of fossil fuels?
Coal
Oil
Gas
What is oil used for?
To make fuel (petrol and diesel) for cars
What is coal used for?
Powering steam trains
Heating
What is gas used for?
Used to heat homes and cook food
What does the combustion of fossil fuels generate?
Generate electricity
What are disadvantages of fossil fuels?
Release CO2 when they’re burnt - contributes to global warming
When coal and oil are burnt, they release sulfur dioxide - causes acid rain
What are the 2 types of non renewable energy resources?
- Fossil fuels
- Nuclear power
How does nuclear power generate electricity?
The nuclear fuel undergoes fission in nuclear reactors - generates electricity
What are disadvantages of nuclear power?
Nuclear waste is dangerous and difficult to dispose of
Carries risk to a major catastrophe e.g. Chernobyl
What are the 5 examples of renewable energy resources?
- Tidal power
- Solar power
- Wind power
- Bio-fuels
- Hydroelectric power
How is electricity generated by tidal power?
- The tide comes in
- Water builds up behind a dam
- The water that’s built up is allowed out through turbines
- These turbines produce electricity
What is a tidal barrage?
A big dam built across river estuaries
What are advantages of tidal power?
No pollution is produced
What are disadvantages of tidal power?
Disturb habitats of nearby wildlife
Spoil the view
Dams are expensive to build
How is electricity generated through solar power?
Solar panels generate electricity when the sun directly hits them
What are advantages of solar power?
No pollution produced
What are disadvantages of solar power?
Don’t work well in the winter or when there’s no sun
What is solar power also used for (not to generate electricity)?
To heat water which is pumped into radiators - heat homes
How is electricity generated through wind power?
Wind turns wind turbines - generates electricity
What are advantages of wind power?
No pollution produced
What are disadvantages of wind power?
Noisy
Spoil the view
Unreliable if there’s no or little wind
How is electricity generated by bio fuels?
Bio fuels are burned - generates electricity
What are bio fuels made of?
Plant products or animal dung
What are disadvantages of biofuels?
Large areas of forest are sometimes destroyed to grow bio fuels - species lose habitats
How is electricity generated by hydroelectric power?
- Big dams are built
- A valley then fills up with water
- The water is then allowed out of the dam through turbines
- This generates electricity
What are advantages of hydroelectric power?
No pollution produced
What are disadvantages of hydroelectric power?
Dams are expensive to build and take up a large area to build
If the valley floods, it can have an impact on habitats and the overall environment
What happened to the demand for electricity in the years 1900-2000? Why?
It increased BECAUSE… population grew & people began to use electricity for more things
What happened to the demand for electricity in the years 2000 onwards? Why?
It’s decreasing BECAUSE… appliances are more efficient & people are more careful with the amount of energy they use up
What are 3 reasons why renewable energy resources are increasing?
- Burning fossil fuels is very damaging to environment - we have discovered this
- We need to learn how to get by without non renewables as they’ll run out (finite)
- There’s pressure on governments and companies to introduce more renewable energy resources
What are the advantages to changing to renewable energy resources?
Less or no pollution produced
They won’t run out
Better for the environment
What are the disadvantages to changing to renewable energy resources?
They’re expensive
Sometimes they’re unreliable - e.g. if there’s no sun, wind, or rain
What are 3 examples of scalar-vector pairs?
- Speed and velocity
- Distance and displacement
- Mass and weight
CORE PRACTICAL: What are all of the components of the equipment used to test the equation F=ma?
Trolley on a ramp that’s attached to a string that’s on a pulley
Masses
Stop clock
Metre rule
CORE PRACTICAL: How to investigate the effect of mass on acceleration using the trolley experiment?
- Get a ramp with a starting line and a finish line, place the trolley behind the line and attach string to it
- Attach the string to a pulley and to the end of the string, add on a hanging mass that’s on a hook
- Once all apparatus is set up, release the trolley from the starting line and start the stop clock
- When the trolley passes the finish line, stop the stop clock
- Calculate the acceleration by using the equation: acceleration = distancex2/time²
- Repeat these steps, each time add another 100g mass to the trolley, until all masses have been added
CORE PRACTICAL: What is the control, independent and dependent variable in the trolley experiment used to investigate the effect of mass on acceleration?
Control: force (weight)
Independent: mass
Dependent: acceleration
CORE PRACTICAL: How to investigate the effect of force on acceleration using the trolley experiment?
- Get a ramp with a starting line and a finish line, place the trolley behind the line and attach string (attached to a hook) to it which is attached to a pulley
- Start with all of the unit masses on the trolley
- Once all apparatus is set up, release the trolley from the starting line and start the stop clock
- When the trolley passes the finish line, stop the stop clock
- Calculate the acceleration by using the equation: acceleration = distancex2/time²
- Then move a mass from the trolley to the hook and repeat steps 3-5 until all masses have been added
CORE PRACTICAL: What is the control, independent and dependent variable in the trolley experiment used to investigate the effect of force on acceleration?
Control: mass
Independent: force (weight)
Dependent: acceleration
CORE PRACTICAL: Conclusion - what’s the effect of mass on acceleration?
Increasing mass decreases acceleration
CORE PRACTICAL: Conclusion - what’s the effect of force on acceleration?
Increasing force applied to the trolley increases acceleration
