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AQA GCSE Physics Unit 3
Transcript of AQA GCSE Physics Unit 3
increase the size of the force
increase the distance from the pivot Centre of mass Centre of mass is the point at which the weight of the object can be said to be acting Symmetrical objects' centre of masses can be found by drawing the lines of symmetry and seeing where they meet Moments can be in balance The principle of moments states that if the
sum of clockwise moment = sum of anti clockwise moment
then the forces are balanced For example, if on one side the moment was 10 cm from the pivot and weighed 5 N, and we had a weight of 2 N to place on the other side, the distance from the pivot it would have to be in order for the moments to equal would be... 5 x 10 = 10 x cm
50 = 2 x m (divide by 2)
cm = 25
25 centimetres from the pivot Stability - tilting and toppling If the centre of mass moves past the pivot, the object will topple. If the centre of mass is not past the object it will move back to its original position. If the centre of mass is in line with the pivot the weight is balanced Circular Motion Objects that rotate or orbit a centre are being held in place by centripetal force. One example of centripetal force is the earth's orbit of the sun Factors that affect centripetal force are
the velocity of the object
the mass of the object
the radius of the circle Turning Forces Gravitational Attraction Newton had three things that he said of gravity
is an attractive force
is bigger the greater the mass of the object
is smaller the greater the distance between two objects
Weight (N) = gravitational field strength (N/kg) x mass (kg) Planetary Orbits Planets usually orbit stars in elliptical orbits, because as the earth gets towards the sun it increases in speed and propels itself further away. Planets are held in their orbit by centripetal force Satellites There are two different types of satellites
A satellite is defined as an object orbiting a planet, meaning that the moon is a satellite. We use artificial satellites for our own needs. Geostationary satellites are used in communications because they stay above the same point on earth, matching it's orbit A polar satellite can be used for weather forecasts, military and move in different directions. They are closer to earth's surface and so can move over the entire earth's surface, every day. Light and Sound Reflection Light can be reflected, with the ray that hits the mirror being called the incidence ray. A convex mirror will present a taller thinner image whilst a concave mirror will present a shorter, broader image. Angle of incidence = angle of reflection Real images are images that are the product of light rays that can be focused onto a scree, whilst virtual images are images that you cannot touch and cannot be projected. Curved Mirrors Concave mirrors are used for magnifying mirrors, that can enlarge your face so that you can see pores. Convex mirrors are used for rear view mirrors in cars because they give a wider view of the surroundings. Refraction