Motion, Forces and Energy Flashcards
How can you find a length?
using a ruler or tape measure
How can you find a volume?
using a measuring cylinder
How can you measure a variety of time intervals?
using clocks and digital timers
centi=
divide by 100
milli=
divide by 1000
kilo=
times by 1000
mega=
times by 1 000 000
giga=
times by 1 000 000 000
What is a scalar quantity?
a quantity that has only magnitude
What is a vector quantity?
a quantity that has both magnitude and direction
What are some scalar quantities?
- distance
- speed
- time
- mass
- energy
- temperature
What are some vector quantities?
- force
- weight
- velocity
- acceleration
- momentum
- electric field strength
- gravitational field strength
What is speed?
distance travelled per unit time
speed formula
v = s/t
What is velocity?
speed in a given direction
formula for average speed
total distance travelled/total time taken
What shows CONSTANT SPEED on a DISTANCE-TIME graph?
a straight, sloping line
What shows A HIGHER CONSTANT SPEED on a DISTANCE-TIME graph?
a straight, sloping line of higher gradient
What shows STATIONARY object on a DISTANCE-TIME graph?
flat/horizontal line
On a distance-time graph, a flat horizontal line means?
the object is stationary
On a distance-time graph, a straight sloping line means?
constant speed
On a distance-time graph, a straight sloping line with a higher gradient means?
higher constant speed
How can you calculate speed from a distance–time graph?
find the gradient
For a speed–time graph, a flat horizontal line at zero speed means?
stationary
When is an object stationary in a speed-time graph?
flat horizontal line at zero speed
For a speed–time graph, a flat horizontal line (>0) means?
constant speed
When is an object in constant speed in a speed-time graph?
a flat horizontal line above zero speed
For a speed–time graph, an upward sloping line means?
accelerating; the steeper the gradient, the higher the acceleration
When is an object accelerating in a speed-time graph?
an upward sloping line
For a speed–time graph, a downward sloping line means?
deceleration
When is an object decelerating in a speed-time graph?
downward sloping line
How can you measure distance in a speed-time graph?
Calculate the area under the speed–time graph
What is the acceleration of free fall g for an object near to the Earth’s surface?
approximately constant and is approximately 9.8 m/s2
What is acceleration?
change in velocity per unit time
formula acceleration
a = ∆v / ∆t
What indicates constant acceleration in a speed-time graph?
a straight line
What indicates changing acceleration in a speed-time graph?
a curved line
How can we calculate acceleration from a speed-time graph?
finding the gradient
What is a deceleration?
a negative acceleration
Describe the motion of objects falling in a uniform gravitational field without resistance.
after dropping, immediately accelerates because gravity pulls the ball downwards
all objects fall with same rate of acceleration, no matter their mass
Describe the motion of objects falling in a uniform gravitational field with resistance.
gravity produces a force pulling downwards, but air resistance pushes back upwards. The more air resistance, the smaller the acceleration.
Eventually, downwards force of gravity is balanced by air resistance, preventing any more acceleration, reaching terminal velocity.
What is terminal velocity?
The top speed reached by any object experiencing air resistance or a similar resistance force.
What is mass?
a measure of the quantity of matter in an object at rest relative to the observer
What is weight?
a gravitational force on an object that has mass
What is gravitational field strength?
force per unit mass, equal to the acceleration of free fall
formula for gravitational field strength
g = W/m
formula for weight
w = mg
How can weights and masses be compared?
using a balance
What is a balance used for?
to compare masses and weights
What is weight, in extended terms?
the effect of a gravitational field on a mass
What is density?
mass per unit volume
Formula for density
p = m/v
How can you determine a liquid’s density?
- place empty measuring cylinder balance and tare the balance
- pour liquid into the measuring cylinder
- record mass from balance and volume from the measuring cylinder
How can you determine a regular solid’s density?
measure mass by balance and volume of shape
How can you determine an irregular solid’s density?
- fill measuring cylinder around half-full with water
- find mass of the object
- measure initial volume of liquid
- place the object into the water. Take a new reading.
- repeat with different starting amounts of water to find its volume
1 cmˆ3 of water =
1ml or 1g
1000 cmˆ3 of water =
1 litre or 1kg
1 mˆ3 of water =
1000 litres or 1000kg
How can we determine whether an object floats?
seeing if its density is bigger than or smaller than water’s (1 g/cmˆ3)
What may forces produce?
changes in the size and shape of an object
If no forces act on it, what occurs to an object?
either remains at rest or continues in a straight line at constant speed
What may a resultant force change?
the velocity of an object by changing its direction of motion or its speed
What is the spring constant?
force per unit extension
formula for spring constant
k = F/x
What is the limit of proportionality? How can we identify it on a graph?
highest force that can be applied before extension of a spring/wire is no longer proportional to force applied, deformation occurs above this point
straight line begins to curve
force =
ma (force and acceleration are in the same direction)
What is solid friction?
the force between two surfaces that may impede motion and produce heating
What will friction act on?
an object moving through a liquid
or a gas (e.g. air resistance)
What is the moment of a force?
a measure of its turning effect
For any system to balance, the clockwise and anticlockwise moments must be ______.
equal
What is the principle of moments?
A system will not rotate if the clockwise and anti-clockwise moments are equal
How can you increase the moment (turning force)?
increase the force or distance from the pivot
What does the moment (turning force) depend on?
size of the force and the distance of the force from the pivot
equation for size of the moment
moment (Nm) = force (N) × perpendicular distance to the pivot (m)
unit for moment
Nm
When is an object in equilibrium?
when there is no resultant force and no resultant moment
Describe an experiment to demonstrate that there is no resultant moment on an object in equilibrium.
- place ruler on glass prism (pivot)
- place pivot underneath centre of the ruler, ensure ruler is balanced
- place mass A 10 cm from pivot, then place an identical mass 10 cm from pivot in other direction, the ruler should balance
- move Mass B so it is further from the pivot, ruler is no longer balanced
What is center of gravity?
imaginary point within an object that the mass and weight of the object is evenly dispersed around
Describe an experiment to determine the position of the centre of gravity of an irregularly shaped plane lamina.
- cut out irregular shape
- make a hole near the edge of the shape and place a pin through it
- clamp pin and make sure card can rotate
- tie a mass suspended by cotton from the pin
- once cotton and card have stopped moving, mark where the cotton is aligned on the card by drawing a line along its length
- repeat, see where lines intersect (centre of gravity)
Describe the effect of the position of the centre of gravity on stability.
centre of mass down low - more stable
centre of mass directly above base - stable
bigger base - more stable
momentum =
mass × velocity
momentum formula
p=mv
impulse =
force × time for which force
acts
impulse formula
impulse = F∆t
impulse = ∆(mv) = (change in momentum)
What happens when two objects collide?
both objects change velocity, some (or all) of the momentum of the first object is transferred to the second
What is conservation of momentum?
in any collision, the total momentum before and after the collision is
the same
What is resultant force?
change in momentum per unit time
formula for resultant force
F= ∆p (momentum) / ∆t (time)
What are different stores of energy?
- kinetic
- gravitational potential
- chemical
- elastic (strain)
- nuclear
- electrostatic
- internal (thermal)
How can energy be transferred between stores?
mechanical work done, electrical work, waves and heat
Example of energy transfer by mechanical work.
forces making things move
Example of energy transfer by electrical work.
electric currents
Example of energy transfer by waves.
light and sound
Example of energy transfer by heat.
such as from a gas cooker
What is the principle of conservation of energy?
energy cannot be created or destroyed, only converted from one store to another
eq. for k.e
k.e = 1/2 mvˆ2
equation for the change in gravitational potential energy
∆Ep = mg∆h
mechanical/electrical work done=
energy transferred
equation for mechanical working
W=Fd=∆E
What are some ways that useful energy may be obtained?
- chemical energy from fossil fuels or biofuels
- water (waves, tides, dams)
- geothermal
- nuclear fuel
- generate electrical power from sunlight
- infrared/other electromagnetic waves from Sun to heat water + be source of wind energy
What energy sources aren’t originally from the Sun?
nuclear, tidal and geothermal
What is the main source of energy for all our energy resources?
radiation from the Sun
How is energy released in the Sun?
nuclear fusion
Advantages/disadvantages of fossil fuels
- high power output, cheap, 24h/per day output
- non-renewable, produces greenhouse gases
Advantages/disadvantages of nuclear
- high power and 24h/day output,
no greenhouse gases - non-renewable,
radioactivity risks, expensive to build
Advantages/disadvantages of hydroelectric
- renewable resource, no greenhouse gases, high power output
- disrupts animal habitats, displaces people, needs a big river, expensive to build
Advantages/disadvantages of tidal
- renewable resource, no greenhouse gases, high power output
- needs high tides (not common) blocks large area of sea,
expensive to build
Advantages/disadvantages of wave
- renewable resource, no greenhouse gases
- new technology, not reliable, low power output
Advantages/disadvantages of solar
- renewable resource, no greenhouse gases
- unreliable, needs sunshine, low power output, expensive to build
Advantages/disadvantages of wind
- renewable resource, no greenhouse gases, cheap to operate
- unreliable, needs wind, low power output per turbine, expensive to build
Advantages/disadvantages of geothermal
- renewable resource, no greenhouse gases, reliable output
- only a few volcanic countries, relatively low power output
What is meant by efficiency of energy transfer?
how much energy isn’t wasted in a system
In what area of energy resources is extensive research being carried out?
investigation on how energy released by nuclear fusion can be used to produce electrical energy on a large scale
efficiency =
(useful energy output) / (total energy input)
Or
(useful power output) / (total power input)
What is power?
work done per unit time or energy transferred per unit time
equations for power
P= W/t
P= ∆E/t
What is pressure?
force per unit area
equation for pressure
p = F/A
Describe how the pressure beneath a liquid surface changes with depth/density of liquid.
the higher/deeper the liquid column, the greater the pressure.
the denser the liquid, the greater the pressure.
equation for the change in pressure beneath the surface of a liquid
∆p = ρg∆h
what is inertia
- property of matter causes it to resist changes in motion until acted upon by an external force
- Newton’s first law of motion - an object with a given velocity maintains that velocity unless acted on by an external force.
- Inertia is the property of matter that makes this law hold true.
why is mass a property that resists changes in motion
The greater the mass of an object, the more difficult it is to speed it up, slow it down or change its direction.
This property of mass is sometimes referred to as inertia
Mass is that quantity that is solely dependent upon the inertia of an object
what is an experiment to determine density of a liquid
measure the mass through a balance and the volume through a measuring cylinder. next, follow the formula to obtain your result
experiment to determine the density of a regular shape
measure the volume by doing the necessary formula and calculations. measure the mass on a scale. divide the mass by the volume
how will you determine if an object sinks of floats
if the density of the object is less than 1 (density of water), it will float. otherwise, it will sink
what is friction
force between two surfaces which impedes motion and results in heating.
formula for force in hooke’s law
force = k (spring constant) x X (extension)
what is a form of friction
air resistance
what is hooke’s law
the displacement or size of the deformation is directly proportional to the force applied.
what is limit of proportionality
the point beyond which Hooke’s law is no longer true when stretching a material
significance of the ‘limit of proportionality’ for an extension–load graph
the object does not return to its original length when the force is removed
what is the law of conservation of momentum
In the absence of external forces (such as friction), the total momentum of a system remains the same
This means that in a collision, the sum of the momentums before the collision will be the same as the sum of momentums after the collision
what is the formula for change in momentum
change in momentum = MVinitial - MVfinal
equation for the conservation of momentum
(m1 x v1) + (m2 x v2) = total mass x V
what are the two formulas for impulse
impulse = change in momentum impulse = force x time
what is the law of conservation of energy
energy can neither be created nor destroyed - only converted from one form of energy to another
what is gravitational potential energy
energy something gains when you lift it up, and which it looses when it falls
what is kinetic energy
energy of a moving object
what is elastic energy
energy of a stretched spring or elastic band
what is chemical energy
energy contained in a chemical substance
what is nuclear energy
energy contained in the nucleus of an atom
what is internal energy
energy something has due to its temperature
what is the formula for kinetic energy
mvˆ2/2
what are the types of energy stores
elastic, chemical, gpe, and nuclear
what are the types of energy transfers
kinetic, thermal, sound, electrical, light
what is internal energy
energy something has due to its temperature
what is the formula for kinetic energy
mvˆ2/2
what is the formula for gravitational potential energy
gpe = mass x gravitational field x change in height
basically, what is work done
energy transferred
what is the formula for work
w = fd
what is power
rate of energy transfer
what is the formula for power
p = energy / time
formula for momentum
mass x velocity
law of conservation of momentum
In any collision, the total momentum before and after the collision is
the same.
impulse =
mvinitial−mvfinal
what is impulse
change in momentum of a system
force in terms of momentum formula
F=change in momentum/change in time
=Δp/Δt
What is the spring constant?
force needed to stretch a spring/wire by one unit of length
