Physics notes for grade 9

1. VOLUME AND DENSITY
VOLUME
• The amount of space taken up
by an object.
• Unit : Cubic metre (m³/ L/ mL)
• Volume changes according to
the external conditions
DENSITY
• Density describes how closely
packed the particles are in a
solid, liquid or gas. Density is the
amount of mass per unit
volume.
• Unit : g/cm³
• Density =
𝑚𝑎𝑠𝑠
𝑣𝑜𝑙𝑢𝑚𝑒

2. WEIGHT VS MASS
WEIGHT
• Force of gravity acting on a
body.
• Unit : Newton (N)
• Depend on the presence of
Earth.
• Can be measured by spring
balance.
• Weight (N) = mass (kg) x gravity
(10N/kg on Earth)
MASS
• The amount of matter it is made
of.
• Unit : Kilogram (kg)
• Mass of a body is same
everywhere (does not depend
on Earth).
• Can be measure by scale balance

3. Gravitational Force
An attractive force that exists between all objects with mass
An object with mass will attracts another object with mass
The magnitude of the force is directly proportional to the masses of the
two objects
“The bigger the mass, the greater the force”
and inversely proportional to the square of the distance between the
two objects.
“ The smaller the distance between the two object, the greater the
force”

4. Spring balance Scale balance
It consists of a spring fixed at one end
with a hook to attach an object at the
other.
Compare the weights of objects or
to weigh objects by balancing them
with standard weights.

5. HEAT AND TEMPERATURE
Heat
• Heat is the flow of thermal
energy.
• Thermal energy - the energy
contained within a system
that is responsible for its
temperature
• Total amount of energy in the
system
Temperature
• How warm or cold something is.
It is the average kinetic energy of
the particles.
• Average amount of energy of a
particle

6. Temperature Change
1. One of the major effects of heat transfer is
temperature changes.
2. Factors that affect how much something will
increase in temperature:
A. Mass of the substance heated – as the mass of the substance
increases, the number of particles in the substance increases. This
means that there are a larger number of particles to heat,
therefore making it more difficult to heat.
B. Type of material – certain materials are easier to heat than
others. For example, we can look at conductors and insulators;
conductors are fairly easy to heat, whilst insulators are difficult to
heat up.
C. Energy input – as the amount of energy input increases, it is easier
to heat a substance. This is because we simply have more energy
available in the system, which can be converted into kinetic energy,
potential energy and thermal energy.

7. Heat transfer
1. The transfer of energy from a warmer object to a cooler object
2. The temperature difference is reduced and both objects end up at
the same temperature.
3. At equilibrium there is no more transfer between thermal stores.

8. The transfer of energy
1. The transfer of energy occur in three ways: through conduction,
convection, radiation and evaporative cooling.
2. Transfer of heat, whether in heating a building or a kettle of water or
in a natural condition such as a thunderstorm, usually involves all
these processes.
 Conduction
• The process by which
heat energy is
transmitted through
collisions between
neighboring atoms or
molecules.
 Convection
• The process of heat
transfer by the bulk
movement of
molecules within
fluids such as gases
and liquids.
 Radiation
• Energy that comes from
a source and travels
through space at the
speed of light. This
energy has an electric
field and a magnetic
field associated with it,
and has wave-like
properties.

9. Conduction
• The transfer of thermal energy through direct contact
• Usually a slow process
• Occurs more readily in solids and liquids
• Heat spontaneously flows along a temperature gradient
• For example, heat is conducted from the hotplate of an electric stove
to the bottom of a saucepan in contact with it

10. Convection
• The transfer of thermal energy through movement of a liquid or
gas
• Heat is transferred by movement of a heated fluid such as air or
water. usually a fairly rapid process.
• Natural convection occurs as air is heated: it expands, rises,
and is replaced by cooler air.
• The amount of convection may be increased by using a fan to
increase the flow of air (Forced convection).

11. Radiation
• The transfer of thermal energy through thermal emission
• the emission or transmission of energy is in the form of waves or
particles through space or through a material medium.
• radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X
rays, and gamma rays.

12. Evaporative Cooling