TOPIC 1- Motion, Forces and Conservation of Energy Flashcards
VECTOR
A quantity with a magnitude and a direction. Can be given as a bearing.
Eg: force, acceleration, velocity, displacement, weight, momentum
Scalar
A quantity with a magnitude but no direction.
Eg: speed, distance, mass energy, temp
Difference between velocity and speed
Velocity is a vector while speed is a scalar. This is because while velocity has a magnitude and direction, speed is simply a magnitude. For example, 2 objects could be travelling at the same speed but at different velocities.
Velocity
Speed in a stated direction
Average Speed equation
Distance travelled/time
M and s
Typical speed of walking Running Cycling Cars on a motorway Aeroplane
1.5m/s 3m/s 6m/s 30m/s 250m/s
What’s centripetal force?
When an object is travelling at a constant speed but is constantly changing direction (velocity), a force acts inwards on the object.
Speed of sound in air
340m/s
Acceleration equation
V-u/ t
Change in velocity/ time
Deceleration
Negative acceleration
Acceleration of gravity in free fall
10m/s^2
What’s acceleration measured in?
M/s^2
Uniform acceleration and its equation
Constant acceleration V squared - u squared = 2 * a * x X = distance A= acceleration V = final velocity U = initial velocity
How do you find the speed of an object in distance time graphs?
Gradient
Change in y/change in x
What do curves show on distance time graphs?
Acceleration
What do you do if the graph is curved?
Draw a tangent and find the gradient of the tangent
How do you find the acceleration on velocity time graphs?
Gradient
What does a curve represent on a velocity time graph?
Change in acceleration
How to find distance travelled on a velocity time graph
Area underneath the graph
What can you use to measure the speed of objects?
Use a stopwatch (human error) over a set distance.
Use a light gate.
Video it
Data logger
Distance
How far a quantity has moved.
SCALAR
Displacement
Distance and direction in a straight line from an object’s starting point to its finishing point.
Speed
How fast you are going
SCALAR
Distance travelled=
(Average) speed * time
Acceleration definition
Change in velocity over a period of time
Uniform acceleration
Constant acceleration
Newton’s first law
If the resultant force on a stationary object is zero, the object will remain stationary. If the resultant force on a moving object is zero, it will just carry on moving at the same velocity.
5 forms of acceleration
Starting Stopping Slowing Speeding up Changing direction
Relationship between force and acceleration
Directly proportional
Acceleration and object mass relationship
Inversely proportional
Formula for Newton’s second law
F = m*a
Force = mass * acceleration
Why are large decelerations dangerous?
Because they require a large force (f=ma), this can be lowered by slowing down the object over a longer time.
Purpose of safety features in vehicles
To increase collision times and so reduce force which reduces risk of injury. (Eg seatbelts/airbags/crumple zones)
Weight
The force acting on an object due to gravity. Caused by gravitational field around earth.
Where does weight exert force on an object?
Its center of mass
Point at which assume whole mass is concentrated
How to measure weight?
Spring balance or Newton meter
Weight =
Mass * gravitation field strength
W = mg
How to investigate motion of trolley on ramp
Measure trolley mass, unit masses, hanging hook, card length.
Mark line on ramp before first light gate (so travels same distance every time)
Attach trolley to hanging mass w string. Let go so it rolls down slope.
Changing ramp height and recording : initial speed, final speed and time between 2 light gates.
What are light gates used for?
Short intervals to rid of human error by reaction times
What can you use to measure distance and time?
Rolling tape measure
Stop watch
Video camera
Inertial mass
The ratio of force over acceleration.
Tendency for motion to remain unchanged.
Newton’s third law
When two objects interact, the forces they exert on each other are equal and opposite.
Action force
The initial force exerted on an object
Normal contact force
The opposite and equal force caused by the action force exerted on the object.
Characteristics of forces in equilibrium
Pairs of forces acting on the same object. (Not Newton’s law).
Eg book is pulled down by weight due to gravity and book pulls back up on earth. Normal contact force from table pushes book up while normal contact force of book pushing down on table.
Momentum=
Mass*velocity
P=mv
What’s momentum measured in?
Kg m/s
What type of force is momentum?
Vector (has size and direction).
Conservation of momentum
In a closed system, total momentum before and event is the same as after an event
What effect do resultant forces have on an object?
Causes them to accelerate
Newton’s 3rd law
When a resultant force acts on an object for a certain period of time, it causes a change in momentum.
Stopping distance
The distance covered between the driver first spotting a hazard and the vehicle coming to a complete stop. Is made up of thinking and braking distance.
Thinking distance
Distance car travels in the driver’s reaction time (time between noticing hazard and applying brakes).
What’s thinking distance affected by?
Reaction time (affected by alcohol, tiredness, drugs, distractions) Speed
Braking distance
The distance taken to stop once the brakes have been applied
What’s braking distance affected by?
Speed
Car mass
Brakes conditions (worn/faulty)
Friction between tyres and road (dirt, ice, wet, bald tyres)
Minimum tread depth of tyres
1.6m
How do you measure reaction time?
Computer based test
Ruler drop test: hang ruler between thumb and forefinger lined up w zero, drop ruler unexpectedly, measurement where you catch demonstrates reaction time, calculate how long ruler was falling for, make average of repeats.
Normal reaction time
0.2-0.6s
Not normal alert driver
Energy in car’s kinetic energy store =
Word done by brakes
1/2 * m* vsquared = f*d
8 types of energy stores
Kinetic Thermal Chemical Gravitational potential Elastic potential Electrostatic Magnetic Nuclear
Kinetic energy =
0.5massvelocity squared
Change in gravitational potential energy=
Massgravitational fs change in vertical height
Conservation of energy
Energy can be stored, transferred between stores, dissipated but can never be created or destroyed.
Total energy of a closed system has no net change.
Closed system
A system that can be treated completely on its own and has no net change in the system’s total energy.
4 methods of transfer
Mechanical
Electrical
Heating
Radiation
Mechanical transfer
A force acting on an object
Electrical transfer
A charge doing work
Heating transfer
Energy transferred from a hotter to a colder object
Radiation transfer
Energy transferred by waves
Total energy input=
Useful energy output + wasted energy
Efficiency =
Useful energy transferred by device/ total energy supplied
Diagram used to show efficiency
Sankey diagram
How do you increase efficiency of a device
Lubrication
Thermal insulation
How does lubrication increase efficiency
Reduce friction between object’s surfaces when move (usually liquids that flow easily between objects to coat them).
Friction transfers energy mechanically to thermal energy stores, dissipated as heat to surroundings.
How does insulation increase efficiency?
Reduces rate of energy transfer by heating.
Lowering thermal conductivity of objects lowers energy transfer through them.
No renewable energy resources examples
Fossil fuels Nuclear fuel (uranium and plutonium)
Advantages of fossil fuels
Reliable
Low cost of extraction
Low cost of factories
Disadvantages of fossil fuels
Slowly running out
Create environmental problems (global warming, acid rain, destruction of animals and their habitats)
Advantages of nuclear fuel
Reliable
Clean
Disadvantages of nuclear fuel
Expensive to build and safely decommission
Nuclear waste is v dangerous and hard to dispose of
Risk of major catastrophe
Renewable energy resources examples
Bio-fuels Wind Solar Hydroelectricity Tidal
Advantages of renewable energy resources
Renewable
Are less damaging to environment
Disadvantages of renewable energy resources
Unreliable
Don’t provide as much energy
Can still do damage to environment
Bio-fuels
Renewable energy resources created from either plant products or animal dung, can be burnt to produce electricity/run cars. SUPPOSEDLY are carbon neutral. V expensive to refine. Forests cleared for bio-fuels result in many species losing natural habitats. Decay increases methane/CO2 emissions.
Wind power
Each turbine has a generator inside which is turned by blades from wind to produce electricity. No pollution. High initial costs w minimal running costs. Produce little energy in comparison to fossil fuels. Can ruin view and be noisy. Unreliable as only work when is windy.
Solar cells
Made from materials that use energy transferred by light to create an electric current. Often used in remote places (can be used for road signs / satellites). No pollution but use much energy to make. Initial costs are high but have no running costs. Smaller scale energy generation. Unreliable as can’t be used at night and are less useful in cloudy countries.
Hydro-electricity
Flooding a valley by building a dam. Rainwater is caught and allowed through turbines (no pollution). Loss of habitat for some species. Can respond immediately to increased energy demand. High initial costs w lower running costs. V reliable.
Tidal barrages
Big dams built across river estuaries w turbines in. As tide comes in, fills up estuary, water then let out at controlled speed to produce electricity. No pollution but affect boat access, spoil view, alter wildlife habitats. Reliable but tide heights vary, barrages don’t work if level is same either side. Moderate initial costs, no fuel costs and minimal costs.
Fossil fuels trend
Over 20th century, UK’s electricity use has hugely increased as did population. Since beginning of 21st century, decreasing slowly as appliances become more efficient and we are more aware of reduction in electricity used. Most generated via fossil fuels & nuclear power. Renewable is now also being used. Fossil fuels also used in heating and car fuels. Biofuels can also fuel cars and solar heaters can heat homes. Renewable sources are being encouraged.
Why is there a push for renewable energy?
As we now know its effects on the environment.
Pressure from public/other countries has led to government putting pressure on energy providers to use more renewable or face business loss.
Car companies using renewable sources and electric cars are becoming more and more popular.
Why is the use of renewables limited?
Building new renewable power plants cost money and are less cost-effective.
Arguments over where renewable plants are built.
Are unreliable
Research into reliability and cost take time and money.
Is expensive to make personal changes.
Minimum number of forces needed to cause a stretch/compression
2
Elastical distortion
Force changing object’s shape before reforming back to original shape/length.
Inelastical distortion
When a force is applied to an inelastic object which doesn’t reform to its previous shape.
Elastic limit
Point at which object stops distorting elastically and begins to distort inelastically.
Where is energy from work done transferred to in an elastic object?
Elastical potential energy store of object.
Hooke’s law
Extension of an elastic object is DIRECTLY PROPORTIONAL to the load/force applied.
Force applied to elastic object formula
K * x
Spring constant * extension
What is the extension in that of a compressed object?
Difference between natural and compressed lengths.
How do you investigate elasticity?
Measure natural length of a spring (w no load applied) *can add markers to spring if necessary.
Add mass to spring and allow to rest before measuring extension.
Repeat
What does elastic distortion display on a graph?
A linear relationship (before limit of proportionality)
Energy stored in a spring formulas
E = 1/2kxsquared E = 1/2 f * x
