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Forces & Motion
Physics (GCSE) Revision (Force&Motion)
|For an object moving at steady speed in a straight line, SPEED =
|DISTANCE / TIME
|Units are metres per second ( m/s )
|If an object moves in a straight line, its distance from a certain point can be represented by . . .
|a distance-time graph
|The steeper the slope the faster the speed.
|When a body is at rest (stationary) its distance-time graph is a . . .
|horizontal straight line.
|It hasn't gone anywhere!
|When a body is moving with constant speed its distance-time graph is a . . .
|diagonal straight line.
|It travels equal distances in equal times.
|The VELOCITY of an object is . . .
|its SPEED in a given DIRECTION
|Velocity is a VECTOR quantity.
|The motion of a body can be represented by a . . .
|Not the same as a distance-time graph.
|On a velocity-time graph, a horizontal straight line represents a body which is . . .
|moving with constant speed in a straight line.
|We also need to know its direction e.g. left to right.
|On a velocity-time graph, a diagonal straight line represents a body moving with . . .
|Its velocity is increasing if the slope is positive.
|If a velocity-time graph shows a curved line then the body is . . .
|changing its acceleration.
|It could be increasing or decreasing the rate at which its velocity is changing.
|The steeper the slope of a velocity-time graph . . .
|the greater the acceleration.
|Think what a rocket does.
|For an object moving in a straight line with a steady acceleration, ACCELERATION=
|change in velocity / time taken for change
|Units are metres per second squared ( m/s^2)
|The gradient of a distance-time graph represents the . . .
|speed of a body.
|Steeper gradient = higher speed.
|The gradient of a velocity-time graph represents the . . .
|acceleration of a body.
|Steeper gradient = greater acceleration.
|The distance travelled by a body can be found by working out the . . .
|AREA underneath a velocity-time graph.
|This is a very useful way to find the distance travelled, especially if the velocity is not constant.
|When the forces acting on an object cancel each other out (balance) the object is in . . .
|It cannot speed up or slow down.
|When an object rests on a surface its weight exerts a downwards force on the surface. The surface will . . .
|exert an equal and opposite force on the object.
|The size of the two forces is the same - they balance.
|Whenever two bodies interact, the forces they exert on each other are . . .
|EQUAL and OPPOSITE
|This is Newton's 3rd law.
|Balanced forces have no effect on the movement of an object. It will either . . .
|remain stationary or if it is already moving, it will continue to move at constant speed in a straight line in the same direction.
|This is Newton's 1st law.
|If the forces acting on an object do not cancel out, an unbalanced force will act. This will cause the object to . . .
|This is Newton's 2nd law.
|Force, mass and acceleration are related by the equation, FORCE =
|mass x acceleration
|This is the usual form of Newton's 2nd law.
|The unit of FORCE (appropriately) is the . . .
|1N gives 1kg an acceleration of 1m/s^2
|If the unbalanced force which acts on a body is kept constant but the mass of the body is increased, the acceleration will be . . .
|acceleration is inversely proportional to mass
|If the mass of a body is constant but the resultant external force increases, the acceleration will . . .
|Acceleration is directly proportional to resultant force.
|If a force of friction acts on a body, the external force needed to give it a particular acceleration will be . . .
|It is necessary to apply a larger force to overcome the effect of the frictional force.
|The direction in which a frictional force acts is always . . .
|in the opposite direction to the motion of a body.
|Friction acts to reduce the speed of a body.
|A force of friction is needed when a car accelerates because . . .
|otherwise the tyres would not grip the road.
|The tyre pushes against the road, which pushes back by Newton's 3rd law.
|Air resistance is a form of friction (drag) which limits the top speed of a racing car because . . .
|when the driving force is equal to the friction force, the two forces are balanced.
|The car has reached TERMINAL VELOCITY
|A sky-diver experiences a frictional drag which increases as his speed increases. The result of this is . . .
|he reaches a terminal velocity and no longer accelerates.
|Newton's 1st law again
|Terminal velocity occurs when . . .
|there is no resultant force acting on a body.
|If forces are balanced, acceleration is zero.
|A force of friction acts when an object moves . . .
|through air or water.
|Also called DRAG
|Friction causes objects to . . .
|heat up and wear away.
|Can be reduced by lubricating with oil or graphite.
|Friction is used to slow down and stop moving vehicles by applying . . .
|Friction between brake pads and wheel drum ( or disks) creates a lot of excess heat energy.
|In order to stop a vehicle moving at high speed we need . . .
|a larger braking force.
|To stop it within a given distance.
|For a given braking force, if a vehicle moves at a higher speed it . . .
|travels further before stopping.
|Stopping distance increases dramatically with increasing speed.
|If too great a braking force is applied, the vehicle may . . .
|Because the wheels will lock and the tyres will slide against the road surface.
|Stopping distance also depends on . . .
|the driver's reaction time.
|If he has taken drugs or alcohol, his reactions will be slower.
|The braking distance depends on . . .
|the speed and road conditions.
|If there is water or ice on the road, the car may skid.
|The faster an object moves through a gas or liquid (fluid) the greater the . . .
|friction or drag acting on it.
|Put your hand out of a moving car window (take care!) and feel the force.
|When a body falls, it accelerates initially due to the force of . . .
|All bodies accelerate at approximately 10 m/s^2 on Earth.
|When a car has a steady speed, the frictional forces balance the . . .
|driving force produced by the engine.
|A bigger engine gives a bigger top speed.
|When a sky diver pulls the ripcord he slows down because the parachute exerts a large . . .
|Initially - but as he slows down this force decreases until it equals his weight.