Physics - Unit 1: Motion, forces and energy

How can length be measured?

Using a ruler

how to measure the volume of a liquid?

using a measuring cylinder

How can length be measured?

Using a ruler

how to measure the volume of a liquid?

using a measuring cylinder

how to measure the volume of a regular solid?

by calculation:

• use a ruler to measure dimensions

• use an appropriate equation to calculate volume

how to find the volume of an irregular solid?

by submersion:

• fill a measuring cylinder with water and read the initial volume

• submerge the object and measure the final volume

• final volume - initial volume = volume of object

how can time be measured?

using clocks or stopwatches

how can the accuracy of measurements be increased?

by taking multiple measurements and calculating the average

what is a scalar quantity?

a quantity with magnitude (size) only

what is a vector quantity?

a quantity with magnitude and direction

what are examples of vector quantities?

• displacement

• force

• weight

• velocity

• acceleration

• momentum

• electric field strength

• gravitational field strength

what are examples of scalar quantities?

• distance

• speed

• time

• mass

• energy

• temperature

how can you measure the resultant of two forces at a right angle

graphically (by drawing each to scale) or by calculation (by Pythagoras or trigonometry)

what is speed?

distance travelled per unit time

what is velocity?

change in displacement per unit time

what is the formula for velocity/speed?

v=ˢ⁄ₜ

what is the equation for average speed?

what is acceleration?

change in velocity per unit time

what is the formula for acceleration?

a=-ᵛ⁻ᵘ⁄ₜ

when does uniform acceleration occur?

when velocity changes at a constant rate

when does non-uniform acceleration occur?

when velocity changes at different rates at different times

what is deceleration?

a negative acceleration

what does a horizontal line represent on a displacement-time graph?

that the object is at rest

what does a straight line with a constant slope mean on a displacement-time graph?

that the object is moving with constant speed

what does a curve upwards mean on a displacement-time graph?

that the object is moving with acceleration

what does a curve downward mean on a displacement-time graph?

that the object is decelerating

what state is the object in when the Y axis is at 0 on the velocity-time graph?

The object is at rest

what does a horizontal line represent on a velocity-time graph?

that the object is moving with constant speed

what does a straight line with a constant slope mean on a velocity-time graph?

that the object is moving with constant acceleration

what does a curve represent on a velocity-time graph?

that the object is moving with changing acceleration

what is the acceleration of free fall g for an object near to the surface of the Earth

• approximately constant

• approximately 9.8 m/s²

how can you calculate the speed of a distance-time graph?

what does the area under the speed-time graph represent?

the displacement

how can you calculate the acceleration of a speed-time graph?

what is mass?

a measure of the quantity of matter in an object at rest relative to the observer

what does the mass of an object resist change from?

its state of rest or motion (inertia)

how can you compare weights and masses?

using a beam balance or equal-arm balance

how can you determine mass?

using an electronic balance

how can you determine weight?

using a forcemeter

what is gravitational field strength?

force per unit mass

what is the formula for gravitational field strength?

g = ʷ⁄ₘ

what is gravitational field strength equivalent to?

the acceleration of free fall

what is gravitational field?

a region in which a mass experiences a force due to gravitational attraction

what is density?

mass per unit volume

what is the formula for density?

ρ=ᵐ⁄ᵥ

how can you measure the density of a regular solid?

• take measurements of relevant dimensions using a ruler

• calculate the volume using an appropriate equation

• measure mass using a balance and calculate density using ρ=ᵐ⁄ᵥ

how can you determine the density of an irregular solid?

• measure volume by submersion: read the volume of the liquid, submerge the solid, then read the change in volume

• measure mass using a balance

• use ρ=ᵐ⁄ᵥ to calculate density

how can you calculate the density of a liquid?

• place an empty beaker on top of a balance and zero the device

• pour liquid into the beaker to determine the mass

• pour the same liquid into a measuring cylinder and read off the volume

• use ρ=ᵐ⁄ᵥ to calculate density

what is weight (gravitational force)?

a gravitational force on an object that has mass

what is drag/air resistance?

the friction of the air on a moving object

what is tension?

force in a string or string being stretched

what is electrostatic force?

the force between two charged objects

what is magnetic force?

attraction or repulsion that arises between electrically charged particles because of their motion

what is thrust?

the force causing an object to move

what is contact force?

a force which acts between objects that are physically touching

what is newton’s first law?

an object either remains at rest or continues to move in a straight line at constant speed unless acted on by a resultant force

how can a force change the velocity of an object?

the velocity of an object by changing its direction of motion or its speed

what is the formula for resultant force?

F = ma

what is newton’s third law?

when object A exerts a force on object B, then object B exerts an equal and opposite force on object A

what does newton’s third law describe

pairs of forces of the same type acting on different objects

what is friction

a force that may impede motion and produce heating

how does an object reach terminal velocity?

• initially, the only force is weight so acceleration is 9.8m/s²

• as it accelerates, speed increases, which increases air resistance

• this decreases the resultant force, so acceleration decreases

• eventually, weight and air resistance are equal and opposite, so there is no resultant force, no acceleration, and terminal velocity is reached

what is thinking distance?

distance travelled during reaction time of driver before the brakes are applied

what is braking distance

distance over which brakes applied before vehicle brought to rest

what is stopping distance

total distance travelled in the time it takes to stop a vehicle

what is the formula for stopping distance?

thinking distance + braking distance

what are the factors that affect thinking distance?

thinking distance is reliant on the driver’s reaction time so factors such as tiredness, alcohol or drug abuse will affect it

what are the factors that affect braking distance

breaking distance becomes longer when the road is wet or icy and there is an increased load carried by the vehicle. however, a deep tyre tread will reduce braking distance

what change may a force produce on an object?

changing the size and shape of an object

what is the spring constant?

force per unit extension

what is the formula for spring constant?

k=F/x

what is the limit of proportionality?

the point where the graph starts to curve away from this straight line

what happens to the motion in a circular path due to a force perpendicular to the motion if the mass and radius are constant?

speed will increase if force increases

what happens to the motion in a circular path due to a force perpendicular to the motion if the mass and speed are constant

if force increases, radius decreases

how do you keep the speed and radius constant during the motion in a circular path due to a force perpendicular to the motion in the case that mass increases?

increase the force

what is the moment of a force?

a measure of its turning effect

what is the equation of the moment of a force?

moment = force × perpendicular distance from the pivot

what is the principle of moments for an object in equilibrium?

when the clockwise moment equals the anticlockwise moment, there is no resultant force. no resultant moment, and the object is in equilibrium.

what is an experiment used to verify the principle of moments?

• pivot a uniform ruler at its centre

• place different masses at different distances from the centre on either side until it balances

• multiply the total mass on either side by 9.81 N/kg to calculate clockwise and anticlockwise moments

• the clockwise and anticlockwise moments will be equal

what is the centre of gravity?

the point at which all of its weight can be considered to act

how to determine the position of the centre of gravity of a plane lamina using a plumb line

• hang up the lamina and suspend a plumb line (thread) from the same place

• mark the position of the plumb line

• repeat with the lamina suspended from different places

• where these lines intersect is the centre of gravity

what is the effect of the position of the centre of gravity on the stability of simple objects

objects with a lower centre of gravity and wider base are more stable

what is momentum and what is its formula?

momentum is mass x velocity, its formula is p=mv

what is impulse and what is its formula?

impulse is force x time, its formula is F△t

what is the principal of the conservation of momentum?

momentum before = momentum after (provided that there are no external forces)

what is resultant force in terms of momentum and what is its formula?

change in momentum per unit time, its formula is F=△p/△t

what are ways in which energy can be stored?

• kinetic

• gravitational potential

• chemical

• elastic (strain)

• nuclear

• electrostatic

• internal/thermal

what is the principle of the conservation of energy?

energy is neither created or destroyed during an energy transfer. it simply changes

what is the formula for kinetic energy?

Ek = (1/2)mv²

what is the formula for the change in gravitational potential energy?

△Ep = mg△h

state 4 ways in which energy could be transferred?

• forces

• electrical currents

• heating

• waves (electromagnetic/sound)

what is the formula for work done?

W = Fd

what are examples of renewable energy sources?

• biofuels

• wind

• hydroelectric and tidal energy

• geothermal energy

• solar power

what are examples of non-renewable energy sources?

• fossil fuels

• nuclear fuels

how can electrical power be generated from the chemical energy stored in fossil fuels and biofuels?

they are burnt to generate electrical power:

• their chemical energy is transferred to heat energy

• the heat energy is used to boil water, creating steam

• the steam turns the turbine

how can hydroelectric resources be used to generate electrical power?

• the water behind the dam is above the ground level, so Ep increases

• Ep gets converted into Ek when water is released down a slope

• the flowing water turns the turbine

how can solar radiation be used to produce electrical power?

solar energy from sunlight is turned into an electric current by solar cells

how do nuclear fuels generate electrical power?

they undergo nuclear fission to produce electrical power:

• thermal energy is released by nuclear fission

• thermal energy is used to boil water, creating steam

• steam turns a turbine

how do geothermal resources generate electrical power?

• as radioactive elements decay, their geothermal energy heats the surrounding rock

• water is poured into shafts in the hot rock

• thermal energy boils the water, creating steam, which is returned via another shaft

• steam turns a turbine

how can wind be used to generate electricity?

as the wind blows, it transfers kinetic energy to the blades of wind turbines

how do the waves and tides in the sea be used to generate electrical power?

the kinetic energy as waves and tides move is used to turn underwater turbines.