ⓉⓄⓅⒾⒸ 1 Flashcards
Mass
● Mass is a measure of how much matter is in an object.
● It is a property that resists change in motion.
weight
● Weight is a gravitational force (the effect of a gravitational field on a mass) measured in
Newtons: 𝑤𝑒𝑖𝑔ℎ𝑡 = 𝑚𝑎𝑠𝑠 × 𝑔𝑟𝑎𝑣𝑖𝑡𝑎𝑡𝑖𝑜𝑛𝑎𝑙 𝑓𝑖𝑒𝑙𝑑 𝑠𝑡𝑟𝑒𝑛𝑔𝑡ℎ = 𝑚𝑔
● The gravitational field strength on Earth is 10Nkg-1
.
● Weights (and hence masses) can be compared using a balance.
Same object on two different planets:
● The mass is the same
● The gravitational field strength g on the two planets will be different (i.e. not 10 for both) so
the weight is different.
Density
● The density is defined as the mass per unit volume: 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 = 𝑚𝑎𝑠𝑠/𝑣𝑜𝑙𝑢𝑚𝑒 𝜌 = 𝑚 𝑉 ● The density ρ is in kilograms per metre cubed, kg/m3 , the mass m is in kilograms, kg, and the volume V is in metres cubed, m3 .
find the density of a liquid:
● Find the mass of the measuring cylinder by placing it on a balance, then fill it with the liquid
and measure the new mass. The difference in masses is the mass of the liquid.
● The volume can be read from the cylinder and the density calculated using the equation.
find the density of solid:
● Measure the mass of the solid by placing it on a balance.
● If the solid is regularly shaped, measure its dimensions using a ruler or other measuring
tool and then use a mathematical formula to find the volume.
● If the solid is irregularly shaped, immerse it in water and measure the volume of the water
displaced. This is the volume of the solid.
● Find the density using the equation
Effects of forces
● Newton’s first law states that an object has a constant velocity unless acted on by a
resultant force.
● Newton’s second law states that 𝒇𝒐𝒓𝒄𝒆 = 𝒎𝒂𝒔𝒔 × 𝒂𝒄𝒄𝒆𝒍𝒆𝒓𝒂𝒕𝒊𝒐𝒏 𝑭 = 𝒎𝒂
● Newton’s third law states that every action force has an equal and opposite reaction force.
For example, the force of the Earth’s gravity on an object is equal and opposite to the force
of the object’s gravity on the Earth.
For an object moving in a circle, with constant speed:
● The speed is constant, but the direction is always changing
● This means the velocity is always changing
● Therefore it is accelerating and there must be a force perpendicular to its velocity
towards the centre of the circle.
● Elastic deformation:
○ The object returns to its original shape when the load has been
● Plastic deformation:
○ The object does not return to its original shape when the load has been removed,
an example being a spring that has been stretched too far.
Hooke’s law states
that for a spring, 𝐹 = 𝑘𝑥 where F is the force applied to the spring in 𝑁, k
is the spring constant in 𝑁𝑚−1
, and x is the extension in 𝑚.
Turning effect
The moment of a force is a measure of its turning effect: 𝑚𝑜𝑚𝑒𝑛𝑡 𝑜𝑓 𝑎 𝑓𝑜𝑟𝑐𝑒 = 𝑓𝑜𝑟𝑐𝑒 ×
𝑝𝑒𝑟𝑝𝑒𝑛𝑑𝑖𝑐𝑢𝑙𝑎𝑟 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑚𝑜𝑚𝑒𝑛𝑡 = 𝐹𝑑
pivot point
is the point which the object can rotate about.
● If a force is applied in the same line as the pivot (see first example in diagram) the object
will not rotate, and will remain stationary
An object is in equilibrium when the(moment)
sum of clockwise moments equals the sum of anticlockwise
moments (the principle of moments) and there is no resultant force.
principle of moments can be applied to check whether something
balances
experiment to show there is no net moment on a body
by pivoting
a uniform ruler at its centre and placing different masses at different distances from the
centre on either side until it balances, and showing that the clockwise and anticlockwise
moments are equal.
Centre of Mass
The centre of mass of a body is the point at which all of its mass can be considered to act. To
calculate the centre of mass of a card:
1. Hang up the card and suspend a plumb line from the same place.
2. Mark the position of the thread.
3. Repeat the above steps with the card suspended from different places.
4. Where these lines intersect is the centre of mass.
Scalars and vectors
● A vector has a magnitude and a direction.
● A scalar has just a magnitude.
scalars
distance, speed, time
vectors
displacement, velocity and acceleration
Vectors can be represented by
arrows. To determine the resultant of
two vectors graphically, they must be
placed head to tail; the line between
the start and finish is the resultant.
Momentum
● Momentum is the product of mass and velocity: 𝒎𝒐𝒎𝒆𝒏𝒕𝒖𝒎 = 𝒎𝒂𝒔𝒔 ×
𝒗𝒆𝒍𝒐𝒄𝒊𝒕𝒚 𝒑 = 𝒎𝒗
● Impulse is the product of force and time, equal to the change in momentum:
𝒊𝒎𝒑𝒖𝒍𝒔𝒆 = 𝑭𝒕 = 𝒎𝒗 − 𝒎𝒖
-In a collision, the total momentum before is equal to the total momentum afterwards, known
as the principle of the conservation of momentum.
-In elastic collisions, the total kinetic energy before is equal to the total kinetic energy after.
Energy transfers
Energy can be transferred between different forms including kinetic, gravitational potential,
chemical, elastic potential, nuclear and internal energy as a result of an event or process.
● Kinetic energy: 𝑬𝒌 =
𝟏/𝟐
𝒎𝒗
𝟐
● Gravitational potential energy: 𝐸𝑝 = 𝑚𝑔ℎ
Energy can be transferred in various ways including:
● Forces
● Electrical currents
● Heating
● Waves
Work is done when
a force moves something through a distance. The work done is equal to the
energy transferred.
● Work done: 𝒘𝒐𝒓𝒌 𝒅𝒐𝒏𝒆 = 𝒇𝒐𝒓𝒄𝒆 × 𝒅𝒊𝒔𝒕𝒂𝒏𝒄𝒆 𝑾 = 𝑭d
Power
r is the rate at which energy is transferred or the rate at which work is done
● Power: 𝑝𝑜𝑤𝑒𝑟 =
𝑒𝑛𝑒𝑟𝑔𝑦 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟𝑟𝑒𝑑/𝑡𝑖𝑚𝑒
efficiency
y is the ratio of the useful work done to the total energy supplied, often
expressed as a percentage.
○ Efficiency: 𝒆𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚 =
𝒖𝒔𝒆𝒇𝒖𝒍 𝒆𝒏𝒆𝒓𝒈𝒚 𝒐𝒖𝒕𝒑𝒖𝒕/𝒕𝒐𝒕𝒂𝒍 𝒆𝒏𝒆𝒓𝒈𝒚 𝒊𝒏𝒑𝒖𝒕 =
𝒖𝒔𝒆𝒇𝒖𝒍 𝒑𝒐𝒘𝒆𝒓 𝒐𝒖𝒕𝒑𝒖𝒕/𝒕𝒐𝒕𝒂𝒍 𝒑𝒐𝒘𝒆𝒓 𝒊𝒏𝒑𝒖t
The efficiency of a system can be increased by:
○ Reducing waste output (lubrication, thermal insulation, etc.)
○ Recycling waste output (e.g. absorbing thermal waste and recycling it as input
energy
Energy sources
-renewable and non-renewable
-It is important to note that apart from geothermal, nuclear and tidal, the sun is the original
source of all energy on earth, released by nuclear fusion.
Renewable
energy is energy which can be replenished as quickly as it is used. Examples include: ○ Biofuel ○ Wind ○ Hydro-electricity ○ Geothermal ○ Tidal ○ Solar ○ Water waves
Non-renewable
energy is used more for large-scale energy supplies due to the large
energy output per kilogram of fuel. Examples include:
○ Fossil fuels (coal, oil, gas)
○ Nuclear fuel
It is usually cheaper than renewable energy but is becoming less popular because one day
it will run out and it is harmful for the environment (e.g. burning fossil fuels releases
greenhouse gases which cause global warming).
Pressure
in fluids causes a net force at right angles to any surface and is measured in Pascals
𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 =
𝑓𝑜𝑟𝑐𝑒/𝑎𝑟𝑒a
The pressure beneath a liquid surface increases with depth and density.
● It is given by 𝒑 = 𝝆𝒈�
A barometer
consists of a tube filled with mercury with a vacuum at
the top. Atmospheric pressure pushes down at the sides causing
the mercury to rise. The height of the mercury is measured to find
atmospheric pressure, where 760 mm or 29.92 in of mercury
corresponds to 1 atm.
A manometer
consists of a U-tube filled with mercury and with a
gas at either end. The difference in the height of the mercury on
either side can be measured to find the pressure difference
between the two ends of the tube.
Length and volume
● A ruler (rule) is used to measure the length of an object between 1mm and 1m.
● The volume of an object of irregular shape can be measured by placing it into a measuring
cylinder full of water. This causes the water level to rise, and this rise is equal to the volume
of the object.
length and time
● A micrometer screw gauge is used to measure very small distances that a rule
cannot measure.
● Analogue and digital clocks and devices are used to measure time intervals.
● An average value for a small distance and for a short time interval can be found by
measuring multiples (including the period of a pendulum).
Motion
● Speed is defined as the distance traveled per unit time. If the speed of something is
changing, it is accelerating. The acceleration of free fall near to the Earth is constant.
velocity
is the speed in a given direction.
Acceleration
is the rate of change of velocity: 𝒂𝒄𝒄𝒆𝒍𝒆𝒓𝒂𝒕𝒊𝒐𝒏 =
𝒄𝒉𝒂𝒏𝒈𝒆 𝒊𝒏 𝒗𝒆𝒍𝒐𝒄𝒊𝒕𝒚/𝒕𝒊𝒎e
distance-time graph:
● The gradient is velocity
○ Negative gradient is returning back to the
starting point
● A horizontal line means it is stationary
● If the distance is zero, it is back at the starting point
● A curved line means that the velocity is changing
and it is accelerating.
In a speed-time graph:
● The gradient is acceleration ○ Negative gradient (i.e. negative acceleration) is deceleration ● If the speed is zero, it is at rest ● A horizontal line means constant speed ● The area under the line is the distance travelled ● A curved line means that the acceleration is changing
