1. Motion, forces and energy (1-8) Flashcards
how to measure a variety of time intervals
analogue clock
digital timer
Determine an average value for a small distance and for a short interval of time by measuring multiples (including the period of oscillation of a pendulum)
(use stop-watch to) time oscillations
(use of fiduciary) aid to determine a complete cycle
(use of) multiple oscillations AND division (to determine period)
Describe scalar and vector quantities with examples
a scalar quantity has magnitude (size) only and a vector quantity has magnitude and direction-
distance, speed, time, mass, energy and temperature
force, weight, velocity, acceleration, momentum, electric field strength and gravitational field strength
Define speed and velocity
distance travelled per unit time; v = s/t
speed in a given direction
Define acceleration
change in velocity per unit time; a=∆v/ ∆t
distance–time graph
(a) at rest
(b) moving with constant speed
(c) accelerating
(d) decelerating
speed–time graph
(a) constant acceleration
(b) increasing acceleration
(c) decreasing acceleration
using speed-time and distance-time to determine
speed from the gradient of a straight line section of a distance–time graph
area under a speed–time graph to determine the distance
acceleration from the gradient of a speed–time graph
acceleration of free fall
acceleration of free fall g for an object near to the surface of the Earth is approximately constant and is approximately 9.8m/s2
Describe the motion of objects falling in a uniform gravitational field with and without air/ liquid resistance (including reference to terminal velocity)
(initially there is acceleration due to) weight OR gravitational force OR unbalanced force / resultant force / downward force
(then) air resistance increases as speed or velocity increases
(as air resistance increases) resultant force downwards decreases OR acceleration decreases
constant speed when air resistance = weight / gravitational force
Define mass, weight and gravitational field strength, equation and how to compare
a measure of the quantity of matter in an object at rest relative to the
observer
weight is a gravitational force on an object that has mass
gravitational field strength as force per unit mass;
g = W/m this is equivalent to the acceleration of free fall
weights (and masses) may be
compared using a balance
density
density as mass per unit volume; ρ = m/V
density of a liquid,
regularly shaped solid
irregularly shaped solid which sinks in a liquid
(volume by displacement)- place it in a measuring cylinder containing water and calculate the change in volume
forces may produce changes in
size and shape of an object
Define spring constant, limit of proportionality and extension
Define the spring constant as force per unit extension; k = F/x
limit of proportionality- up to this limit, the extension on a load is proportional to load. this is Hooke’s law.
extension- increased length of an object when load is attached to it
curves and slopes up less steeply, not proportional it is permanently damaged and deformed so won’t return t its original position once the load is removed.
force eqn
F = ma and the force and the acceleration are in the same direction
resultant force and object’s motion
an object either remains at rest or continues in a straight line at constant speed unless acted on by a resultant force
a resultant force may change the velocity of an object by changing its direction of motion or its speed
Describe, qualitatively, motion in a circular path due to a force perpendicular to the motion
(a) speed increases if force increases, with mass and radius constant
(b) radius decreases if force increases, with mass and speed constant
(c) an increased mass requires an increased force to keep speed and radius constant
Describe friction in solid, liquid and gas
force between two surfaces that may impede motion and produce heating ( slows the object down and causes an increase in thermal energy)
friction (drag) acts on an object moving through a liquid
friction (drag) acts on an object moving through a gas (e.g. air resistance)
Describe moment
Describe the moment of a force as a measure of its turning effect and examples- tap, door handle, scissors
moment = force × perpendicular distance from the pivot
principle of moment
if an object is balanced, the total clockwise moment about pivot equals the total anti-clockwise moment
Equilibrium conditions
when there is no resultant force and no resultant moment, an object is in equilibrium
Describe an experiment to determine the position of the centre of gravity—-
State what is meant by centre of gravity
Describe, qualitatively, the effect of the position of the centre of gravity on the stability of simple objects
the point at which the object’s weight may be considered to act/ concentrates.
if the centre of gravity is lower and base is wider, the object is more stable
Define momentum, impulse, resultant force
momentum as mass × velocity; p = mv
impulse as force × time for which force
acts; impulse = F∆t = ∆(mv)
resultant force as the change in momentum per unit time;
F = ∆p/∆t
state the principle of conservation of momentum
the total momentum is constant and does not change because of an interaction between bodies such as collisions
whenever two objects interact, the total amount of momentum before they interact is the same as the total amount of momentum afterwards.
energy may be stored as
kinetic, gravitational potential, chemical, elastic (strain), nuclear, electrostatic and internal (thermal)
Describe how energy is transferred between stores during events and processes
transfer by forces (mechanical work done), electrical currents (electrical work done), heating, and by electromagnetic, sound and
other waves
principle of the conservation of energy
Energy cannot be created or destroyed, it can only be stored or transferred. total amount of energy before and after transfer is constant.
What is equal to energy transferred
mechanical or electrical work done.
W = Fd = ∆E
Define efficiency
(%) efficiency = (useful energy output)/ (total energy input) (× 100%)
(%) efficiency = (useful power output)/(total power input) (× 100%)
radiation from the Sun is the main source of energy for all our energy resources except and how is energy from sun released
geothermal, nuclear and tidal
energy is released by nuclear fusion in the Sun
Describe how useful energy may be obtained, or electrical power generated, from—
(a) chemical energy stored in fossil fuels
(b) chemical energy stored in biofuels
(c) water, including the energy stored in waves, in tides, and in water behind hydroelectric dams
(d) geothermal resources
(e) nuclear fuel
(f) light from the Sun to generate electrical power (solar cells)
(g) infrared and other electromagnetic waves from the Sun to heat water (solar panels) and be the source of wind energy
Describe advantages and disadvantages of each method in terms of renewability, availability, reliability, scale and environmental impact—-
Define power
work done per unit time and also energy transferred per unit time;
P = W/t
P = ∆E/t
Define pressure
force per unit area. p = F/A
weight from heeled shoes is spread over a smaller area which exerts a higher pressure.
how the pressure beneath the surface of a liquid changes with depth and density of the liquid
∆p = ρg∆h gravity is constant so more depth and more density= more pressure
