Topic 2 Flashcards
When will a body move in a circular path
If it’s motion is at right angles to a force that acts inwards along the radius of path
A body moving in a circular part with constant speed still has a?…
Changing velocity
What’s the force acting in words along the radius of the circle called
Centripetal force
What are the four main centripetal forces
Gravitational
Frictional
Tension
Electrostatic
Example of gravitational force
Orbiting satellite
Example of frictional force
Car on a roundabout
Example of tension force
Hammer thrower
Example of electrostatic force
Electron orbiting the nucleus
Equation for momentum
Momentum = mass x velocity
Kg m/s. Kg. M/s
P = m x v
Equation for force not needed to remember
Change in momentum / time taken for the change
F = mv - mu/ t
When the mass or the deceleration of a vehicle are large, the Forbes exerted on the passengers…
Are also large this can be v dangerous
Car safety features such as seat belts and crumple zones do what?
Revise the size of the forces on the driver and pssengers by increasing the time over which the vehicle comes to rest
Changing the time changes the force needed to change the momentum. By increasing the time over which the change in momentum takes place… the force…
Needed is reduced
What does Newton’s third law relate to
Bodies in equilibrium and can be applied to collisions when considering the conservation of momentum
What does Newton’s third law state
That for every action there is an equal and opposite reaction.
The action force and the reaction force act on different bodies
In Newton’s third law the reactants have to be
Reacting on different bodies
When a truck and car collide, they exert equal and opposite forces on each other are in contact for same amount of time. Newton’s 3rd law is obeyed.
Momentum…
Is conserved : the total momentum before the collisions equals the total momentum afterwards
What is human reaction time
The time between a stimulus occurring and a response.
Related to how quickly the human brain can process information and react to it
What’s a typical human reaction time
Between 0.2 s and 0.25 s
What can affect reaction time of humans
Tiredness
Alcoholic and drugs
Distractions
Age
How can you determine human reaction time
Using the ruler drop test
Equation for reaction time
= √ 2 x distance ruler falls/gravity
Explain why the reaction time doubled when the distance that a ruler falls increases by a factor or 4
Reaction time Is proportional to the square root of the distance an object falls. The square foot of 4 is 2 so four times the distance means twice the reaction time
What is stopping distance
The total distance over which a vehicle comes to rest
Equation for stopping distance
= thinking distance + braking distance
What’s thinking distance
The distance the car travels while the driver reacts to the danger and applies the brakes
What’s braking distance
The distance the car travels while it is slowing down
What happens to thinking and braking distance when the cars speed increases?
They increase
When you double the speed of the car what happens to the thinking distance ?
It doubles
What factor does the breaking distance increase by?
4
Thinking distance increases when:
The driver is tired
The driver is distracted
The driver has taken alcohol or drugs
Braking distance increases when
The amount of friction between the tyre and road decreases
To road is icy or wet
The brakes or tyres are worn
The mass of the car is bigger
Thinking distance is what to the speed?
Directly proportional
Braking distance is proportional to
(Speed)^2
What’s the equation that governs a force applied to the brakes, the kinetic energy is transferred to thermal energy and the vehicle comes to rest over a certain distance
F x d = 1/2 x m x v^2
What are the eight main energy stores
Chemical Kinetic Gravitational potential Elastic Thermal Magnetic Electrostatic Nuclear
Example of chemical energy store
Fuel
Food
Battery
Example of kinetic energy store
Moving objects
Example of gravitational potential energy store
Raised mass
Example of elastic energy store
Stretched spring
Example of thermal snergy store
Hot object
Example of magnetic energy store
Two magnets
Example of electrostatic energy store
Two charges
Example of nuclear energy store
Radioactive decay
What’s a closed system
One where energy can flow in or out of the system but there is no transfer of mass
Eg pan with lid on
What happens to the net change in an a nervy transfer in a closed system
There is no net change
What are the four ways that energy can be transferred
Mechanically
Electrically
Thermally
Radiation
How is energy transferred mechanically
By a force moving through a distance
How is energy transferred electrically
By the use of electric current
How is energy transferred thermally
Because of a difference in temperature
How is energy transferred by radiation
By waves such as electromagnetic or sound
The rate at which thermal energy is transferred through a wall of a house depends on :
The difference in temperature between the warmer interior and the colder exterior
Thickness of walls
Material walls are made from
How can unwanted energy transfers be reduced
By thermal insulation and lubrication
A material with high thermal conductivity is a better conductor of energy than
One with a lower thermal conductivity
Different material have different
Relative thermal conductivities
A verycefficient machine has an efficiency that is nearly
100%
Equation for efficiency
Useful energy/total energy x 100
Main energy resources include both
Renewable and non renewable resources
What are renewable energy resources
They will not run out
Most do not cause pollution or emit carbon dioxide
Examples of renewable energy resources
Bio-fuels Hydroelectricity Wind turbines Tidal power Solar cells
What are bio-fuels
Animal or plant matter used to produce thermal energy, electrical energy or used to power cars
What’s hydroelectricity
Generated electricity from water behind a dam flowing down a pipe and turning a turbine to generate electricity
What are wind turbines
Use kinetic energy from the wind to generate electricity
What’s tidal power
Used the rise and fall of the tide or tidal currents to generate electricity
What’s solar cells
Convert solar energy, or energy from the sun, directly to electricity. Solar energy can also be used directly to cook food or heat water
What are non renewable resources
Are resources that will run out eventually
Examples of non renewable resources
Fossil fuels
Nuclear fuels
They are available all the time unlike some renewable resources
Fossil fuels…
Are coal, oil and natural gas They are used: To generate electricity To power transport To hear homes and for cooking
Nuclear fuels…
Such as uranium are used:
To generate electricity
As energy sources in spacecraft
Describe how different renewable and non-renewable resources are used for transport
Renewable and non-renewable energy resources can both be used in power stations, leading to the production of electricity which is used to power trains. Electrical energy can also be supplied from other renewable sources such as solar, hydroelectric and wind
Biofuel in the form of methanol is an example of how renewable fuel can be used to power cars and solar power is also being developed to do more of this. Petrol and diesel, from oil, are examples of non- renewable fuels that are used to power cars
What’s inertial mass
A measure of how difficult it is to change the velocity of an object (including from at rest) and know that it is defined as the ratio of force over acceleration
What are the factors which have caused the use of energy resources changing over the years
•The worlds population
-in the last 200 years pop went from 1 bill to 7 bill-
•the development of technically
-cars trains and planes and other devices have increased in number and all require energy-
• electrical energy
-power stations require fuels in order to generate electricity-
What is most of the worlds energy
Fossil fuels
Fossil fuels are a finite reserve so will run out and not be replaced. Greater use of fossil fuels will lead too…?
More carbon dioxide in the atmosphere
There will be greater global warming leading to severe weather flooding and threats to food supplies
Main issues with using the earths energy supplies
Threats to food supplies to those who need them
Global warming and floods due to using fossil fuels
Running out of non renewable resources
Wood is a biofuel. Suggest why wood had been used constantly for many years whereas other fuels have only been used much more recently
Wood has been readily available for thousands of years and has not had to be discovered, minds or have any extra technology developed in order for it to be used to produce thermal energy
Explain how force is related to momentum
Force is the rate of change of momentum
It’s the change in momentum divided by time taken
KE is proportional to
V^2
