Triple Physics

GCSE Physics Triple Revision Cards 2011

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Forces and Energy: circular motion and centripetal

Circular Motion: It is the result of two forces (one force being the centripetal force - towards the centre of the circle - the other force is tangential force - provided by the means of propulsion of the mass). The centripetal force is greater if the mass and speed is greater, but becomes less if the radius is greater. Formular is: Force= mass x velocity(squared) divided by radius

Centripetal force pulls on an object in circular motion towards the centre of the circle and has to be present

Centrifugal force is an illusion caused by the perception that such an object is attempting to move in a radial direction

Gravity: universal force of attraction between two masses, and is greater if those masses are greater and is less if the distance is between them is greater. Earth and Moon orbit each other because of gravity. They are accelerating towards each other but also have a tangential motion, the result being motion in orbits. Planets in the solar system have orbits that are elliptical, with the Sun at one focus. The further a planet is from the Sun, the greater its period of orbit.

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Forces and Energy: circular motion and centripetal

When an artificial satellite is put into orbit there is a precise connection between the height of the satellite above the Earth and the correct speed to keep it in orbit. The greater the height, the less the speed to keep it in orbit. This means that a low orbiting satellite has a relatively high speed, taking only an hour or to so to orbit the Earth. Such satellites are useul for applications such as imaging of land and weather systems.

There is one particular height at which the speed means that the satellite is orbiting the Earth once every 24 hours. If it is arranged that this is in the same direction that the Earth is rotating then, relative to a fixed point on the earth, the satellite appears to be stationary (also known as geostationary). Such satellites are particularly useful when it comes to telecommunications as they provide a continuous link, and weather images from these satellites will cover a larger area than the polar orbiting ones.

A comit has an orbit that is often highly elliptical; as it approaches the Sun its speed increases, and as it heads off further out again, the speed decreases.

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Forces and Energy: momentum, impact and collisions

Momentum is possessed by a moving object and is what will keep moving. It is proportional to mass and velocity. A car travelling at a greater speed has more momentum than one travelling at a slower speed. However, it has less momentum than a heavy truck travelling at the same speed due to its larger mass. Momentum is calculated as the product of mass and velocity = mass x velocity

In an impact between two objects, each exerts the same force on the other. Force is equal to the rate of change in momentm. As momentum is a product of mass and velocity, the impacting objects will not rebound with equal speeds (unless the masses are identical and initial velocities equal and opposite). Injury is caused to bodies in a road traffic accident due to the rate of change in momentum: if this is reduced , such as by the use of crumple zones or air bags, it means that the force upon the body is less.

Momentum is conserved in an impact: the total momentum after the collision is the same total momentum before.

Collisions - a collision of 2 vehicles, the impact is elastic and the total momentum afterwards is the same as that before

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