Physics: P4, P5, P6

Physics: P4, P5, P6Revision cards

Velocity tells you an objects speed and direction of travel. For example if a lorry travels along a road at 15m/s in one direction the velocity is +15m/s but if it travels the opposite direction at the same speed the velocity is -15m/s. Changes in distance is described as positive but the opposite direction is negative.You can work out the speed of an object by working out the gradient of a displacement-time graph. First chose two paints the calculate.Dis(1)-Dis(2)Time taken between both

The instantaneous velocity of an object is its instantaneous speed together with an indication of direction.The slope/gradient of a speed time graph shows how quickly an object is accelerating. The steeper the faster its speed increases. They're used in lorry tachographs so the dont exceed speed/ rest for suitable time. Straight line which isn't on zero means its constant.The quantity velocity has both speed/direction. A change of either/both will change the velocity. Velocity can become negative if an object is going in the opposite direction.A force is the interaction between two objects. Whenever one exerts force it always experiences force back. The forces in an interaction are equal and opposite. A person apply force to the earth we can walk because our mass is lighter. Some forces only occur as a response to another force. i.e. when an object is on a surface gravity pulls it down and the surface pushes up. (reaction of surface)The slope/gradient of a distance time graph is a measure of speed . The steeper he slope, the greater he speed.Physics: P4revision cardsTobi Ojo12TTo calculate an objects average speed you need to know the distance and time. The speed of an object at a particular point is the instantaneous speed.

Explaining motionIf the resultant force acting on an object is zero its momentum wont change. i.e. if the object is stationary it will stay stationary, if its moving it will continue to move. Collisions can cause change in an objects momentum. Sudden changes in momentum car affect a car/people. If the change of momentum is spread over a period of time the resultant will be smaller. Safety device: crumple zone.When two objects try to slide past each other they both experience the force friction. Arrows are used to represent force the bigger the arrow the bigger the force. Also the direction of the arrow shows the direction the force is working.Acceleration= changing in speed (m /s2) time taken (s)Momentum is a measure of the motion of an object. If a lorry and a car travel at the same speed the lorry will have more momentum.

Momentum = mass x velocity

If the gradient is steeper than the dashed line then its faster vice versa.

Cars and bicycles have a driving force produced by the engine/energy also they have counter force caused by friction. Bigger driving force speeds up. Equal driving force constant, smaller driving force slows down.

A moving object has kinetic energy. The amount depends on its mass/ velocity. The greater the mass/ velocity the greater the kinetic energy. Kinetic energy=1/2 x mass x velocity^2When a ball is thrown two forces oppose it which are: air resistance and gravity causing the ball to lose speed. i.e. when a skydiver jumps forces are unequal but become equal/constant.Work results in the transfer of energy an object either loses or gains energy. Overall the energy stays the same (conserved). Energy gain can be less because some energy may be dissipated.

Work done (j) = force (N) x distance moved (m)When an object is lifted off the ground work is done by lifting force against gravity. (gravitational potential energy) Change in GPE (j) =weight x vertical height difference If the GPE is 100J loses the kinetic energy would be 100J gains.

Components resist the flow of charge through them i.e. resistors, lamps, motors. The wire have a little resistance but since its so small its ignored. The greater the resistance the smaller the current. 2 lamps in a circuit have a certain resistance but when you add another cell (battery) you increase the potential difference and the current.When you add resistors in series the resistance increases because the battery has to push charges. When you add resistors in parallel the resistance decreases because of the many paths. (current increase). When electric current flows through a component it makes it heat up this is enough to make a lamp filament glow. Moving charges collide with vibrating ions (energy)As long as a components resistance stays constant, the current through the resistor is directly proportional to the voltage.The resistance of a thermistor is dependent on temperature. When the temperature increases its resistance decreases and more current flows. The resistance of a light dependent resistor (LDR) depend on light intensity. When the amount of light falls its resistance decreases and more current flows.When your rub two objects together they become electrically charged as electrons are transferred. The object receiving electrons becomes negative vice versa. When two objects are brought together they exert force two which are different attract vice versa. An electrical current is a flow of electricity (amps). In an electrical circuit the wires/component all have a charge. The battery causes the free charges to move.Charges aren't used up but flow continuously. In metal conductors there are lots of free charges but in insulators there are none. Direct current (d.c) always flows in one direction. Alternating current (a.c) changes the direction of flow back used for main supply of voltage to our homes. Potential difference=voltage. Potential difference between two points is work.Avoltageis produced when a magnet is moving into a coil of wire. (electromagnetic induction). The direction of the induced voltage is reversed when the magnet is moved out of the coil again. It can also be reversed if the other pole of the magnet is moved into the coil. To increase the induced voltage: Move magnet faster, Use stronger magnet, Increase the number of turns on the coil, Increase the area of the coil. Generators use the principle of EI.

The greater potential difference the greater current also happens when you add more batteries. When you add more batteries to a parallel circuit the PD and current stay the same each battery supplies less current. a.c is used for main supplies instead of d.c since its easier to generate, can be distributed efficiently, only a.c can be used in a transformer.The current that flows in each component connected in series is the same. The circuit diagram shows a circuit with two lamps connected in series. If one lamp breaks, the other lamp will not be lit. When two or more components are connected inseries, the same current flows in each component.

If one lamp breaks, the other lamp will still be lit. Because a parallel circuit has more paths for charges to flow along, the current is bigger, and the resistance of the whole circuit is smaller.When two or more components are connected inparallel, the total current flowing in the circuit is shared between the components.Pyhsics :P5revision cardsTobi Ojo12TElectrical circuitsThepotential differencesacross resistors in series must add up to the batteryvoltage.In parallel circuits, the voltage across each component is the same as the voltage of the battery.

when electrical charge flows through a component work is done. Energy is transferred from the power supply to the components/surroundings. Power is the rate of energy transferred. Transformers are used to change the voltage of an a.c it consist of 2 coils which when near induces voltage. A transformer that increases the voltage is called astep-up transformer.A transformer that decreases the voltage is called astep-down

A simple electric motor can be built using a coil of wire that is free to rotate between two opposite magnetic poles. When an electric current flows through the coil, the coil experiences a force and moves.The direction of the current must be reversed every half turn, otherwise the coil stops. You can use a commutator.

Electric motors are used in hard disk drives, DVD players, tumble dryer etc.

Pyhsics :P6revision cardsTobi Ojo12TRadioactive materialsSources of background radiation: medical x rays, food, gamma rays from rocks/soil, radon gas and cosmic rays from outer space. An atoms activity drops whilst it decays meaning its radioactivity decreases. The half-life is the times taken for the substances radioactivity to halve. Different substances vary in half-life. A substance is considered safe once its activity has dropped to the same level as background radiation.Sievert is a measure of a radiation doses potential to harm. Gamma rays can help kill cancer cell but may damage healthy cells doctors must weigh out the risks/ benefits.Radiation can be used to: sterilise surgical equipment/food, PET scans.Nuclear power stations release energy because of the changes of nucleus of radioactive substances this is nucleus waste. High-level waste isnt radioactive for long so they store it for a short time. Intermediate-level waste remains radioactive for years hard to store (concrete) . Low-level waste slightly radioactive and sealed/placed in landfills. Nuclear power stations dont release pollutants.Radioactive decay:Unstable Alpha= new nucleus + a particle Unstable beta= new nucleus + b particleUnstable gamma= stable gamma + gamma radiation.Background radiation is radioactive elements found naturally in the environment. If a person is irradiated their exposed if their contaminated radioactive material has entered them.Radioactive materials can give out three Ionising radiation: alpha, beta, gamma. They all have different penetrating powers. Least penetrating to most (Alpha, beta, gamma/paper, aluminum, sheet of lead) ionizing radiation emitted when the nucleus is unstable then decays (radioactive decay) this process helps the atom become stable.Nuclear fission: when a neutron hits an unstable nucleus splitting it and creating energy this continues to happen like a chain reaction. (uranium and plutonium) Nuclear power stations use fission reactions to generate heat. The nuclear reactor control the chain reaction. Fission takes place in the fuel rods (boron) which heat up moving them changed the amount of fission.All elements are made of atoms. All contain a nucleus and electrons. The nucleus is made from protons and electron except hydrogen (1 proton, 1 electron) Radioactive elements emit ionizing radiation nothing can stop this behavior. Every element has a particular number of protons except isotopes. For example oxygen.Ionising radiation can break molecules into ions they can damage living cell to the point they die or become cancerous. Alpha can be dangerous if inside the body cells will absorb the radiation. Beta rays can be dangerous if outside the body unlike alpha it can penetrate the outer layer. Gamma can pass through the body and cause little damage.Marsden and Rutherford concluded that all atoms consisted of empty space and a nucleus. The nucleus is positively charged and electrons are arranged around.