# Physics Sumary P2

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• Created by: Lucy1499
• Created on: 10-04-16 14:49
• Physics Summary P2
• Forces and energy
• A resultant force shows the combined effect of several forces. It makes an object accelerate.
• The speed of an object can be found using a distance time graph. The acceleration and distance travelled can be found using a velocity time graph
• Objects gain gravitational potential energy if they are lifted up. Moving objects have kinetic energy. Stretched or squashed elastic objects store elastic energy
• The stopping distance of a vehicle is thinking distance plus braking distance
• Moving objects reach a terminal velocity (top speed) when drag forces matches driving forces
• Momentum is mass X velocity. It is conserved when objects collide or explode apart if no external forces act.
• A force transfers energy when it does some work on an object
• Static Electricity
• Insulating materials can be charged by rubbing. They gain or lose electrons
• Objects carrying the same charge repel. Objects carrying the opposite charge attract
• Electrical circuits
• Electric current is a flow of charge
• In a series circuit: the current is the same throughout, the potential difference is shared between components and the resitance of components adds
• Circuit diagrams use standard symbols
• Resistance measures how easily a current flows through a component. Resistance = potential difference    current
• In a parallel circuit, the current is shared between branches and the potential difference is the same for each branch
• Using mains electricity safely and the power of electrical appliances
• Batteries supply direct current; mains supply is alternating at about 230V 50Hz
• Electric cable can be two-core or three-core. A three pin plug must be correctly wired
• Energy transferred is the potential difference supplied X charge
• Earthing, fuses and RCCBs protect the user and appliance
• Power is the potential difference supplied X current, or energy transferred   time
• An atomic nucleus contains protons and neutrons. Electrons orbit the nucleus. Radioactive materials emit ionising radiation from their nucleus
• Half-life is the time taken for the count rate of a radioactive sample to halve
• Alpha, beta, and gamma radiation have different properties, uses and dangers
• Background radiation comes from natural sources (e.g. rocks) and man made sources like medical uses
• Ions are atoms that have lost or gained electrons. Isotopes have the same number of protons, but different numbers of neutrons
• Nuclear fission and nuclear fusion
• Nuclear fission is the splitting of an atomic nucleus
• Fission of uranium- 235 or plutonium-239 during a chain reaction releases energy in nuclear reactors
• All stars have a life cycle. Nuclear fusion in stars releases energy and produces all naturally occurring elements
• Nuclear fusions is when two atomic nuclei join to form a larger one