1. Motion, Forces and Energy Flashcards
1.1 Physical quantities and measurement techniques 1.2 Motion 1.3 Mass and weight 1.4 Density 1.5 Forces 1.6 Momentum 1.7 Energy, work and power 1.8 Pressure
Average speed (m/s)
Total distance travelled (m) / Total time taken (s)
Speed (symbols)
v = s/t
Acceleration (m/s²)
Change in velocity (m/s) / time taken (s)
Acceleration (symbols)
a = Δv/Δt
Change in Velocity
Final velocity - initial velocity
Gradient
Increase in y-axis / Increase in x-axis
Gradient (rule)
Rise/run
Gradient of a distance-time graph
speed
Gradient of a speed-time graph
acceleration
Area under a speed time graph
Distance
Acceleration of free fall (g)
The acceleration of a body falling under gravity. 9.8 m/s²
Terminal velocity
The top speed reached by any object experiencing air resistance or a similar resistance force.
Velocity (m/s)
displacement (m) / time (s)
Velocity (symbols)
V = Δx/Δt
Mass
A measure of the amount of matter in an object
Weight (unit)
A measure of the force of gravity on an object (Newtons)
Gravitational field strength
Gravitational field strength N/kg = weight (N) / mass (kg)
Gravitational field strenth (symbols)
g = W/m
Density (f)
mass/volume
Density
The mass of an object per unit volume
Density of water
1 g/cm3
Force
A push or pull exerted on an object
Force (N)
mass (kg) * acceleration (m/s²)
Spring constant
A measure of a spring’s resistance to being compressed or stretched
Spring constant
Spring constant (N/m) = Force (N)/Extension (m)
Limit of proportionality
The limit for Hooke’s law applied to the extension of a stretched spring
Moment (Nm)
Force (N) * Perpendicular distance to pivot (m)
Equilibrium
A body is in equilibrium if there are no net forces and no net moments. (balanced)
Centre of Gravity
The imaginery point within an object that the mass and weight of the object is evenly dispersed around (also known as the centre of mass).
Line of symmetry
If a shape can be reflected about any line without changing the shape, the object has ‘line symmetry’ and the line used is called the line of symmetry.
Momentum (def)
The product of the mass and velocity of an object. The units are kg m/s.
(The oomph of an object)
Momentum (formula)
p = mv
p - momentum (kgm/s)
m - mass (kg)
v - velocity (m/s)
Conservation of momentum
The natural law that the total momentum of a system of objects after a collision is the same as the total momentum before the collision, as long as there are no external forces acting on the system.
Elastic Collision
READ KOGNITY ELSA AND DONT BE LAZY
Inelastic Collision
READ KOGNITY ELSA AND DONT BE LAZY
Impulse (def)
The change in momentum of a body, usually caused by a collision or impact.
Impulse (formula)
ΔP = FΔt
ΔP = Impulse (kgm/s)
F = Force (N)
Δt = Change in time (s)
ΔP = mv - mu
Impulse = final momentum - initial momentum
Impulse = change in momentum
(Both formulas work and can be used)
Ft = mv - mu
Conservation of energy
In an isolated system the total energy remains constant. Energy cannot be created or destroyed, only converted from one store to another.
Energy transfer
Energy is moved from one store to another when work is done.
Gravitational potential store of energy
The energy stored in an object lifted upwards in a gravitational field.
Kinetic energy
Energy stored in a moving object.
Gravitational potential energy
The energy stored in an object lifted upwards in a gravitational field.
Energy stores (types)
Kinetic
Gravitational Potential
Chemical Potential
Elastic Potential
Nuclear
Electrostatic
Thermal (internal kinetic)
Energy Transfers (types)
Mechanical (Forces)
Electrical
Heating
Electromagnetic (Sound or other waves eg light.)
Kinetic Energy (formula)
Ek = 1/2mv²
Ek = Kinetic Energy ( J )
m = mass (kg)
v = speed (m/s)
Gravitational Potential (formula)
Ep = mgΔh
Ep= Gravitational Potential ( J )
m = mass ( kg )
Δh = change in height (m)
Work (def)
Work done is the energy transferred to an object when a force moves the object over a distance.
Work (formula)
W = Fd
W = Work ( J )
F = Force (N)
d = distance (m)
W = ∆E
Work = Energy Change
Power (def)
The rate at which energy is transferred, measured in watts.
Power (formula)
P = W / t
P = Power (W)
W = Work ( J )
t = time (s)
P = ΔE / t
P = Power (W)
ΔE = Change in energy ( J )
t = time (s)
Energy efficiency (formula)
(useful energy/total energy) * 100
Pressure (formula)
P = F/A
Pressure (Pa)
Force (N)
Area (m²)
Liquid pressure (formula)
P = pgΔh
P = Pressure (Pa)
p = Density (kg/m³) <– Needs to be kg/m³ for Pa
g = gravitational field strength (9.8 m/s²)
Δh - Change in depth (m)
How do you measure liquids in a measuring cylinder?
Look at the bottom of the meniscus (curve of the liquid).
Scalar
A measurement with a size (magnitude) and no specific direction.
Vector
A quantity with a size (magnitude) and a direction.
Scalar (examples)
Distance, Speed, Time, Mass, Energy and Temperature.
Vector examples
Force, Weight, Velocity, Acceleration, Momentum, Electric field strength, Gravitational field strength
Speed
The distance travelled per unit time.
Acceleration
The rate of change of velocity of a body, measured in m/s2.
Circular motion
You need a force to act at right angles (perpendicular) to motion to make an object turn in a circle.
For an obect moving in a circular path, more force is needed if…
- The mass of the object increases
- The speed of the object increases
- The radius of the circle decreases
Friction
A force between two surfaces when in contact. It impedes motion and results in heating.
Moment
A turning force.
Principle of moments
A system will not rotate if the clockwise and anti-clockwise moments are equal.
Gravitational + Kinetic Energy
1/2 mv² = mgh
1/2v² = gh
Efficiency of power input / output
Efficiency = (useful power output / power input) * 100%
Pressure
A measure of the compression, or ‘outward push’ from a substance. It is defined as the force per unit area.
Fuel Power Plants
Most energy comes from burning fuels (usually fossil fuels ( coal, oil or gas )) Burning the fuel transfers the energy from the chemical store to heat.
- Source of heat (fuel) is used to boil water.
- As the water boils, it turns into a high pressure steam.
- The steam flows through pipes to turn a turbine.
- After the steam has spun the turbine, it is cooled in a condeser and reenters the boiler system as water to be used again.
Nuclear (Energy source)
A nuclear power plant is similar to a coal / gas power station, but instead of burning a fossil fuel, it uses a nuclear reaction to produce energy.
Pros
- No CO2 or other greenhouse gases produced.
- Each kg of fuel contains large amounts of energy (high energy density)
Cons
- Uranium is a finite resource and so it is non-renewable.
- Nuclear power produces radioactive waste, which is difficult to dispose of and can damage local environments if not dealt with properly.
- There is a small risk of nuclear accidents. However, the consequences of an accident are very severe, causing death and disease to humans and animals and contaminating the area for a long time.
- Because of stringent safety precautions and complex machinery, power plants are expensive and take a long time to build. They are also extremely expensive to decommission (take apart once they are past their lifetime).
Hydroelectric (Energy resources)
This involves building a dam wall on a river. By holding the water behind the wall, a large height difference can be achieved between the water upstream and downstream. Hydroelectric power relies on the water rushing downstream, through pipes with turbine blades, which generate electricity
Pros
- The water always flows, so electricity can be produced 24 hours a day.
- No carbon dioxide or other greenhouse gases produced.
- Renewable - the water is constantly replenished by rainfall.
Cons
- When the dam is first built it floods large areas of land, which damages or destroys habitats and homes.
- The flow of water downstream of the dam can be reduced, which can sometimes change or destroy habitats.
Tidal (Energy resources)
Tidal power uses the same principle as hydroelectric power, but instead of trapping river water, it traps seawater behind a dam (barrage) wall. Water at high tide is trapped behind the barrage to produce a flow of water through turbines, which generate electricity.
Pros
- The flow of tides is a naturally recurring process. This is a renewable resource.
- No carbon dioxide or other greenhouse gases produced.
- Tides are easy to predict.
- High power output.
Cons
- Only some places have big enough tidal changes to produce sufficient electricity in this way.
- Tidal dams and machines can damage marine ecosystems and habitats.
- Blocks large areas of the sea.
Wave (Energy resources)
Wave power uses the movement of waves up and down to drive turbines, and to produce electricity.
Pros
- Renewable, Sustainable + no greenhouse gases
- Good energy conversion
- Simple maintenance
- Good in remote areas
Cons
- May damage wildlife + ecosystem.
- Coastal erosion rates may increase
- Weak in bad weather
- High maintenance costs.
Solar (Energy resources)
Solar panels are black surfaces that absorb infrared electromagnetic waves from the Sun to heat water for homes.
Solar cells produce electricity directly from electromagnetic waves in sunlight. This can be transmitted through power lines to homes across the world.
Pros
- Ecofriendly
- May increase value of your home
Cons
- Weather dependent (needs sunlight)
- Expensive
- Producton may be harmful to the environment
- Takes up a lot of space.
Wind (Energy resources)
Wind turns the turbines.
Pros
- The wind is a renewable resource - it will not run out.
- No carbon dioxide or other greenhouse gases produced.
- Turbines are comparatively easy and cheap to produce.
- Once the turbines are built, the wind has no cost, you only need to pay for maintenance.
Cons
- Some people think they look and sound unpleasant.
- You need a lot of turbines to produce a significant amount of power, so they need to be spread over a lot of land or sea.
- Some days are windier than others, so the wind power is unpredictable.
Geothermal (Energy resources)
If you live a country with volcanic activity, such as Iceland or Japan, you may know that it is possible to tap into the hot rocks underground. Cold water is fed through pipes underground and returns as steam due to the volcanic activity. The steam drives turbines to generate electricity.
Pros - Ecofriendly
Cons - Restricted locations
How does the sun get its energy + extra?
Nuclear fusion takes place in the sun. Currently we are trying to figure out how to do that.
Most of our energy comes from the sun. Plants use sunlight for food –> Animals use plants for food –> both become fossil fuels –> used in combustion. Also wind and wave energy is produced by the sun heating hte atmosphere and producing convection currents.
Which energy resources do not originate from the sun?
Nuclear power - Energy comes from within atoms.
Tidal power - Motion of the sea caused by gravity between the moon and the earth.
Geothermal power
Which energy resources do not originate from the sun?
Nuclear power - Energy comes from within atoms.
Tidal power - Motion of the sea caused by gravity between the moon and the earth.
Geothermal power - Comes from hot rocks underground, and is tapping into the internal energy stored in molten rocks deep in the Earth.
Fuels (Pros + Cons)
Pros
- high power output
- 24 hours a day output
- cheap to build
Cons
- non-renewable
- produces greenhouse gases
centi (c)
÷100
milli (m)
÷1000
kilo (k)
×1000
mega (M)
×1000000
giga (G)
×1000000000
1cm² = ? m²
1cm² = 0.0001 m²
Newtons 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, it 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)
Newtons second law
F = ma
Newtons third law
Whenever two objects interact, they exert equal and opposite forces on each other.
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