Studied by 0 people
Scalar and vector quantities
Scalar quantities have magnitude only. Vector quantities have magnitude and direction. A vector quantity may be represented by an arrow. The length of the arrow represents the magnitude, and the direction of the arrow the direction of the vector quantity.
north= up
south = down
west=left
east=right
Contact and non-contact forces
A force is a push or pull that acts on an object due to the interaction with another object. All forces between objects are either: • contact forces – the objects are physically touching • non-contact forces – the objects are physically separated. Examples of contact forces include friction, air resistance, tension and normal contact force. Examples of non-contact forces are gravitational force, electrostatic force and magnetic force. Force is a vector quantity. Students should be able to describe the interaction between pairs of objects which produce a force on each object. The forces to be represented as vectors.
gravity
Weight is the force acting on an object due to gravity. The force of gravity close to the Earth is due to the gravitational field around the Earth. The weight of an object depends on the gravitational field strength at the point where the object is. The weight of an object can be calculated using the equation: weight = mass × gravitational field strength W = m g weight, W, in newtons, N mass, m, in kilograms, kg gravitational field strength, g, in newtons per kilogram, N/kg (In any calculation the value of the gravitational field strength (g) will be given.) The weight of an object may be considered to act at a single point referred to as the object’s ‘centre of mass’.The weight of an object and the mass of an object are directly proportional. Weight is measured using a calibrated spring balance (a newtonmeter).
Resultant forces
A number of forces acting on an object may be replaced by a single force that has the same effect as all the original forces acting together. This single force is called the resultant force. Students should be able to calculate the resultant of two forces that act in a straight line. (HT only) Students should be able to: • describe examples of the forces acting on an isolated object or system • use free body diagrams to describe qualitatively examples where several forces lead to a resultant force on an object, including balanced forces when the resultant force is zero. (HT only) A single force can be resolved into two components acting at right angles to each other. The two component forces together have the same effect as the single force. WS 1.2 (HT only) Students should be able to use vector diagrams to illustrate resolution of forces, equilibrium situations and determine the resultant of two forces, to include both magnitude and direction (scale drawings only).
Work done and energy transfer
When a force causes an object to move through a distance work is done on the object. So a force does work on an object when the force causes a displacement of the object. The work done by a force on an object can be calculated using the equation: work done = force × distance moved along the line of action of the force W = F s work done, W, in joules, J force, F, in newtons, N distance, s, in metres MS 3b, c Students should be able to recall and apply this equation. One joule of work is done when a force of one newton causes a displacement of one metre. 1 joule = 1 newton-metre Students should be able to describe the energy transfer involved when work is done. WS 4.5 Students should be able to convert between newton-metres and joules. Work done against the frictional forces acting on an object causes a rise in the temperature of the object.
Forces and elasticity
The extension of an elastic object, such as a spring, is directly proportional to the force applied, provided that the limit of proportionality is not exceeded. t f orce = s pring constant × extension F = k e force, F, in newtons, N spring constant, k, in newtons per metre, N/m extension, e, in metres, mf orce = s pring constant × extension F = k e force, F, in newtons, N spring constant, k, in newtons per metre, N/m extension, e, in metres, m MS 3b, c, 4a Students should be able to recall and apply this equation. This relationship also applies to the compression of an elastic object, where ‘e’ would be the compression of the object. A force that stretches (or compresses) a spring does work and elastic potential energy is stored in the spring. Provided the spring is not inelastically deformed, the work done on the spring and the elastic potential energy stored are equal. Students should be able to:
• describe the difference between a linear and non-linear relationship between force and extension
• calculate a spring constant in linear cases MS 3b, c, 4a • interpret data from an investigation of the relationship between force and extension WS 3.5 • calculate work done in stretching (or compressing) a spring (up to the limit of proportionality) using the equation: elastic potential energy = 0.5 × s pring constant × extension 2 Ee = 1 2 k e²
Moments, levers and gears (physics only)
A force or a system of forces may cause an object to rotate. Students should be able to describe examples in which forces cause rotation. The turning effect of a force is called the moment of the force. The size of the moment is defined by the equation: moment o f a f orce = f orce × distance M = F d moment of a force, M, in newton-metres, Nm force, F, in newtons, N distance, d, is the perpendicular distance from the pivot to the line of action of the force, in metres, m. If an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment about that pivot. Students should be able to calculate the size of a force, or its distance from a pivot, acting on an object that is balanced. A simple lever and a simple gear system can both be used to transmit the rotational effects of forces. Students should be able to explain how levers and gears transmit the rotational effects of forces.
difference between speed and velecity
speed = scalar so have magnitude
velocity= vector magnitutde + direction soutj east west or north
distance and displacement
distance is scalar with out direction
displacement is a vector so it includes direction
force
a push or pull motion
change of shape like stretching a spring
changing the speed
change the direction
types: contact and noncontact and measures using newtons
contact
they are touching
friction oposes objects two sliding surfaces
air resistance drag acts on object moving trhough the air
tension forces exerted on an object that is pulled
normal e.g a forces holding you up when you sit on a chair
non contact
act between object that are physically separated
gravity pulls earth downwards
electrostatic forces act between charged objects
magnetic when a magnetic atracts or repels an object
weight
the name given to the pull of gravity
earth’s gravitational pull is 9.8
so each kg is pulled 9.8
free body space diagrams
shows a swuare with arrows facing the direction that the force acts and is the same length as the force e.g 1cm is 1 n
resolving forces
use a² +B² = c²
or SOHCAHTOA
work done
force X distance
work done is measured in joules
forces and elasticity
forces in balance can change the shape of something when:
when they are balanced and stretched a spring
and they are balanced and compress a beam
or three balanced forces bend a beam
when something is stretched past the constant inelastic deformation occurs and it can’t go back to its normal size e,g mr Herring practical.
it goes back to its normal size its simply elastic deformation
limit of porportionality
when a spring is permanently deformed
moments levers and gears
a spanner is used to creat a larger turneing effect to undo bolts and nuts . the turning effect is the moment
principle of moments
sum of anticlockwise moment = sum of clockwise moment
Note
Flashcard