# Physics

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How do you calculate acceleration?
Acceleration (m/s2) = Change in velocity (m/s) / Time taken for the change (s)
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What is terminal velocity?
Terminal velocity is the constant speed reached by any falling object when the air resistance is equal to the force of gravity.
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How do you calculate weight?
Weight (N) = Mass (kg) x Gravitational Field Strength (N/kg)
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What is inertia?
The inertia of an object is its resistance to a change of motion. The greater the mass of an object, the more inertia it has.
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How do you calculate density?
Density (kg/m3) = Mass (kg) / Volume (m3)
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How do you measure the density of an irregular solid?
Measure the mass of the object by using an electronic balance. Then, use a displacement can to measure the volume of the solid. Density = Mass / Volume
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What is Hooke's law?
Hooke's law for springs states that the extension of a spring is directly proportional to the weight it supports until the limit of proportionality.
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What is the limit of proportionality?
The limit of proportionality is the limit to which a spring can be stretched an still obey Hooke's law.
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What is the resultant force?
The resultant force is a single force that has the same effect as all the forces acting on the object.
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How do you calculate the resultant force?
Resultant Force (N) = Mass (kg) x Acceleration (m/s2)
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What is centripetal force?
Centripetal force is the resultant force of an object moving in circular motion. It acts towards the centre of the circle.
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How do you calculate the moment of a force?
Moment (Nm) = Force (N) x Perpendicular Distance to Pivot (m)
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What is the Principle of Moments?
The sum of all the clockwise moments about any point = The sum of all anticlockwise moments about any point. This applies for an object in equilibrium.
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Define Centre of Mass.
Every object behaves as if its mass were concentrated at one point. This point is called the centre of mass.
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How do you increase stability?
The stability of an object is increased by making its base as wide as possible and its centre of mass as low as possible. An object will tend to topple over if the line of action of its weight is outside its base.
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What is the difference between a vector and a scalar?
A vector has direction whereas a scalar quantity does not. Examples of vectors include velocity, acceleration and weight. Examples of scalar quantities are mass, speed, energy and power.
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How do you calculate efficiency?
Efficiency = The useful energy used by the device / The total energy supplied to the device.
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What is nuclear fission?
Nuclear fission occurs when a uranium nucleus splits as a result of being struck by a neutron. Energy is released in nuclear fission.
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What is nuclear fusion?
Nuclear fusion occurs when two nuclei are forced close enough together so they form a single larger nucleus. Energy is also released in nuclear fusion.
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Describe how wind energy works.
A wind turbine is an electricity generator at the top of a narrow tower. The generator is driven by the force of the wind on its blades.
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Describe how wave energy works.
A wave generator at a coastal site uses the motion of waves to make a floating section move up and down. This motion drives a turbine which turns a generator.
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Describe how hydroelectricity works.
Hydroelectricity is generated when rain water collected in an uphill reservoir flows downhill. The water flow drives turbines that turn electricity generators at the foot of the hill.
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Describe how tidal energy works.
A tidal power station traps each high tide and uses it to turn generators.
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Describe how solar energy works.
Solar energy can be converted into electricity using solar cells or used to heat water directly in solar heating panels.
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Describe how geothermal energy works.
Geothermal energy is released by radioactive substances deep inside the earth. As a result, heat energy transfers outward towards the Earth's surface. Rocks below the surface become very hot. Water -> Steam which drives the turbines and generators.
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How is work calculated?
Work Done (J) = Force (N) x Distance (m)
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How is chance of gravitational potential energy calculated?
Gravitational Potential Energy (J) = Mass (kg) x Gravitation Field Strength (N/kg) x Height (m)
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How is kinetic energy calculated?
Kinetic Energy (J) = 0.5 x Mass (kg) x Velocity Squared (m/s)
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How is power calculated?
Power (W) = Energy Transferred (J) / Time Taken (s)
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How is pressure calculated?
Pressure (Pa) = Force (N) / Area (m2)
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Give examples of pressure being used in mechanics.
Hydraulic break systems, robots and car jacks.
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How is pressure in a liquid changed?
The pressure of a liquid increases with depth. The pressure in a liquid increases with density.
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How is pressure of a liquid column calculated?
Pressure (Pa) = Height (m) x Density (kg/m3) x Gravitational Field Strength (N/kg)
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How is a U-tube manometer used?
The pressure of the gas forces the liquid in the manometer up the open side of the U-tube until it is at rest. The height difference between the two levels is a measure of the pressure of the gas.
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How is a mercury barometer used?
An increase of atmospheric pressure causes the mercury to rise in the tube. A decrease of atmospheric pressure causes the mercury to fall.
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What causes the pressure of a gas?
The pressure of the gas on a surface is caused by its molecules repeatedly hitting the surface.
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How does temperature affect gas pressure?
The pressure of a gas in a sealed container increases if the gas temperature is increased.
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What is Brownian motion?
Brownian motion is the erratic motion of microscopic particles due to random impacts of gas molecules on each particle. The air molecules must be moving very fast to cause this effect because they are far too small to see and the smoke particles big.
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What is the difference between saturated and unsaturated?
If all the water in the bowl evaporates, and the air in the room can still "hold" more water vapour, the air is said to be unsaturated. If a bowl containing sufficient water is left in a room, evaporation occurs until the air is saturated.
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How do you increase the rate of evaporation?
Evaporation from liquid can be increased by increasing the temperature or surface area of the liquid or by creating a draught of air across its surface.
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What is Boyle's law.
Boyle's law means that the pressure varies in inverse proportion to the volume of the gas.
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Which of these states of matter expand more thermally?
Gases expand much more than liquids or gases.
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How are volume and temperature of a gas related?
The volume of a gas at constant pressure increases when its temperature is increased.
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What is the specific heat capacity of a substance?
The specific heat capacity of a substance is defined as the energy needed to raise the temperature of 1kg of the substance by 1 degree Celsius.
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What is the latent heat of fusion?
The latent heat of fusion is the energy supplied to a substance to melt it; also, energy removed from a substance to solidify or freeze it.
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What is the latent heat of vaporisation?
The latent heat of vaporisation is the energy supplied to a liquid substance to vaporise it; also, energy removed from a vapour to liquefy it.
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What is convection?
Convection is the transfer of energy in a liquid or a gas due to a temperature difference causing circulation within the liquid or gas.
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What is conduction (heat)?
Conduction of heat is the transfer of energy due to a temperature difference within a substance as a result of vibrations of atoms in any substance and the movement of free electrons in a metal.
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Which surfaces are the best emitters and absorbers of infra-red radiation?
Dark, matt surfaces emit and absorb infra-red radiation better than light, shiny surfaces.
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How is wave speed calculated?
Wave Speed (m/s) = Frequency (Hz) x Wavelength (m)
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What are transverse waves?
Transverse waves vibrate at right angles to the direction of travel of the waves. Electromagnetic waves are transverse waves.
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What are longitudinal waves?
Longitudinal waves vibrate parallel to the direction of travel of the waves. Sound waves and compression waves along a slinky spring are longitudinal waves.
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What is refraction?
Refraction is the change of direction of waves when they cross a boundary due to a change in the speed of waves.
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What is diffraction?
Diffraction is the spreading of waves when they pass through a gap or round an obstacle. For noticeable diffraction the gap must be similar in size to the wavelength. The narrower the gap, the more the waves spread out.
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When is refraction towards or away from the normal?
Refraction is towards the normal when light travels from air to glass (less dense to more dense). Refraction is away from the normal when light travels from glass to air (more dense to less dense).
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What is the refractive index?
Refractive Index (n) = The Speed of light in air / The speed of light in the substance = sin i / sin r
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What happens when an object is two focal lengths away from a converging lens?
If the object is two focal lengths away then the image height will be equal to the object height.
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What happens when an object is between one and two focal lengths away from a converging lens?
The image is real, upside down and bigger than the object. This only happens if the object is between 1 and 2 focal lengths away from the lens.
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What happens when an object is less than one focal length away from the converging lens?
The image is virtual, upright and magnified when an object is less than one focal length away from the lens.
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How do you calculate magnification?
Magnification = Image Height / Object Height
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What are electromagnetic waves?
Electromagnetic waves are electric and magnetic disturbances that transfer energy from one place to another.
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Describe sound waves.
Sound waves are longitudinal waves which consist of alternate compressions and rarefactions when passing through air.
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In which state of matter does sound travel the fastest?
Sound travels the fastest in solid, then liquid and then gas.
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What happens when you rub a perspex rod with a dry cloth?
Rubbing a perspex rod with a dry cloth transfers electrons from the surface atoms of the rod onto the cloth. So the perspex rod becomes positively charged.
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What happens when you rub a polythene rod with a dry cloth?
Rubbing a polythene rod with a dry cloth transfers electrons to the surface atoms of the rod from the cloth. So the polythene rod becomes negatively charged.
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How do you calculate charge?
Charge (C) = Current (A) x Time (s)
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How do you calculate potential difference?
Potential Difference (V) = Electrical Energy Supplied (J) / Charge (C)
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How do you calculate resistance?
Resistance (Ohms) = Potential Difference (V) / Current (A)
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How can the resistance of a wire change?
The resistance of a wire depends on the material it is made from and is proportional to its length and inversely proportional to its area of cross-section.
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How do you calculate power?
Power (W) = Energy transformed (J) / Time taken (s)
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How do you calculate electrical energy supplied?
Electrical Energy Supplied (J) = Current (A) x Potential Difference (V) x Time (s)
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How do you calculate electrical power?
Electrical Power (W) = Current (A) x Potential Difference (V)
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What is a capacitor?
A capacitor is a device designed to store charge. Energy is stored in a charged capacitor.
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## Other cards in this set

### Card 2

#### Front

What is terminal velocity?

#### Back

Terminal velocity is the constant speed reached by any falling object when the air resistance is equal to the force of gravity.

### Card 3

#### Front

How do you calculate weight?

What is inertia?

### Card 5

#### Front

How do you calculate density?