Download 12.2 Forces and Motion Keywords Acceleration

12.2 Forces and Motion Keywords
Acceleration - change in speed divided by time.
Velocity - speed in a particular direction.
Constant velocity - speed in a direction that has the same direction and the same value.
Speed - distance covered in a period of time.
Velocity time graph - a graph in which velocity (vertical axis) is plotted against time (horizontal axis).
Ticker Timer - a machine that prints 50 dots a second onto a paper strip. You can work out the speed from
this. One interval is 1/50 sec – 0.02s
Stationary - something that is standing still. (NB: Stationery - paper, pens, etc.)
Directly proportional - a graph goes up in a straight line from the origin.
Inversely proportional - the graph is a 1/x graph, called a hyperbola.
Gradient - the steepness of the slope. Gradient = rise ÷ run = y / x
Force - push, pull, or twist.
Newton - unit of force.
Weight - a force acting on an object caused by gravity
Friction - force opposing movement caused by surfaces rubbing against each other.
Air resistance - drag experienced by moving through air.
Drag - resistance to movement through a fluid.
Terminal velocity - the maximum downwards velocity of an object falling through a fluid.
Streamlined - long thin shape that allows an object to pass through a fluid with the least possible drag.
Density - mass per unit volume, or how heavy something is for a given volume.
Upthrust - upwards force that results from the action of a fluid. It opposes the weight.
Equal and opposite force - forces that are equal in value but opposite in direction
Force meter - instrument to measure force.
Triangle of forces - a diagram showing the way that three forces act.
Vector – has magnitude, unit and direction – e.g. velocity and displacement
Scalar – has magnitude and no direction – e.g. speed and distance
Component - a force can be split into two perpendicular force vectors.
Resolving - turning a force vector into two perpendicular force vectors.
Resultant force - force that occurs on an object when two or more forces are applied.
Parallelogram rule – Used to find the resultant of two vectors
Direction - towards a particular point.
Gravity - an attractive force that pulls objects to the Earth.
Gravitational field strength - is the force acting on a mass due to gravitational attraction - force per unit
mass. The Earth’s gravitational field strength is 10 N / kg – W = mg
Acceleration of free fall – downwards acceleration due to gravity value near to the Earth’s surface is
10 m / s2 for IGCSE
Mass - amount of material in an object
Braking distance - distance covered by a car when the brakes are on.
Reaction time - time taken for a driver to see an emergency, and apply his foot on the brake.
Stopping distance - the total distance from when a driver sees an emergency to the car coming to a stop.
Thinking distance - the distance covered by the car as the driver is reacting to an emergency.
Circular Motion
Centripetal (centrifugal = no marks)
Centripetal acceleration - acceleration towards the centre of a circle
Centripetal force - force acting towards the centre of the circle
Uniform Circular Motion – an object moving at a steady speed, while continuously changing direction with
a constant radius, has uniform circular motion
Velocity - speed with a direction.
Accelerate - change of velocity – which can be a change in speed or direction
Friction - a force that opposes movement.
Resultant force - overall force resulting from all other forces.
Tension - a pulling force.
Tangent - a straight line that touches a curve perpendicular at a point
For example, if you remove the centripetal force, by cutting the string that holds a stone in circular motion,
the stone will move off in a straight line, at a tangent to the circle.
Moments & Centre of Mass
Moment - the turning effect of a force
Anticlockwise moment - a moment that goes anticlockwise
Clockwise moment - a moment that goes clockwise
Resultant moment - the turning effect of all the forces
Turning effect - how a force makes an object turn.
Pivot - the central point, pin, or shaft on which a mechanism turns or oscillates.
Fulcrum the point against which a lever is placed to multiply force, or on which it turns, or is supported
Centre of mass - an imaginary point around which all the mass is thought to act. (In a uniform gravitational
field, such as on earth, this is the same as the centre of gravity.)
Centre of gravity – an imaginary point through which all the weight of an object seems to act.
Force - a push, pull, or twist
Gravity – an attractive pulling force between masses
The Principle of Moments - when an object is in equilibrium, the sum of the anticlockwise moments about
a turning point must be equal to the sum of the clockwise moments. sum of anticlockwise moments =
sum of clockwise moments
Equilibrium - object is in balance; it is not toppling over. When there is no resultant force and no resultant
turning effect, a system is in equilibrium
Neutral Equilibrium – an object, whose centre of mass stays over its base, may roll, but not topple.
Stability - how likely an object is to remain standing. A stable object has a wide base and a low centre of
mass.
Stable - cannot be pushed over easily.
Stable equilibrium – when tipped a little, an object will return it is original position if the centre of mass
stays over the base.
Unstable - will tip over easily
Unstable equilibrium - how a force makes an object turn
Hooke’s Law
Elastic materials return to their original shape when the forces on them are removed.
Plastic materials retain their new shape, when forces are removed
Hooke’s Law - The extension of a spring or wire is directly proportional to the force applied provided the
limit of proportionality is not exceeded.
Spring constant is the gradient of the force (x- axis) against extension (y-axis) the gradient is the spring
constant Units N/m
A stretching force puts an object such as a wire or spring under tension
The limit of proportionality is the is the point beyond which Hooke’s law is no longer true when stretching
a material.
The elastic limit is the point beyond which the material you are stretching becomes permanently stretched
so that the material does not return to its original length when the force is removed.
A squashing force puts an object under compression.