# Physics Unit 2 Summary notes

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Physics Unit 2

o   Topic 1

o   Gradient on a distance-time graph = speed

o   Long-distance vehicles are fitted with recorders called Tachographs, to check that drivers don’t drive too long

o   Velocity is speed in a given direction

o   The acceleration(m/s2) of an object is its change of velocity per second

o   Constant speed

o   Gradient on a velocity-time graph = acceleration

o   The area under the line on a velocity-time graph = distance travelled

o   Topic 2

o   A force can change the shape of an object or change its motion or its state of rest

o   When 2 objects interact they always exert equal and opposite forces on each other

o   Force is measured in newtons (N)

o   engine force / motive force due to friction

o   Resultant Force = the combined effect of the forces acting on an object

o   If resultant force = zero, object remains stationary / constant velocity

o   Thrust, air resistance, friction

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o   The greater the mass of an object, the smaller its acceleration is for a given force

o   High speed, poor weather conditions (icy) and poor maintenance (brakes and tyres) all increase the braking distance.

o   Poor reaction time (tiredness, alcohol, drugs and mobile phones) and high speed both increase the thinking distance.

o   The gravitational force of attraction slightly weaker at the equator than at the poles

o   Weight = The force of gravity on an object

o   Mass = The quantity of matter in an object; a measure of the difficulty of changing the motion of an object

o   If an object falls with no other forces acting on it, the resultant force on it is its weight. It accelerates downwards at a constant acceleration of 10m/s2

o   fluid drags on an object

o   drag force increases with speed

o   acceleration of an object decreases as it falls, because the drag force increases as it speeds up, so the resultant force decreases, so the acceleration decreases

o   when drag force = weight , reaches constant velocity called terminal velocity, and the resultant force is zero, so the acceleration is zero

o   The terminal velocity of a falling object is the velocity it reaches when it is falling in a fluid. The weight is then equal to the drag force on the object.

o   An elastic object regains its shape when the forces deforming it are removed

o   Hooke’s Law; The extension of a string is directly proportional to the force applied, provided its limit of proportionality is not exceeded

o   The spring constant of a spring is the force per unit extension