Physics: Chapter 8 - Transfer of Thermal Energy

8.1 Transfer of Thermal Energy
Thermal energy always flows from a region of higher temperature to a region of lower temperature.

8.2 Conduction
Conduction is the process of thermal energy transfer without the medium flowing.
Occurs mostly in solids, good conductor of heat.

Thermal energy is supplied to a material -> Particles at hot end vibrate vigorously -> Particles collide with neighbouring particles -> Kinetic energy is transferred to the neighbouring particles.
This happens because metals contain many free electrons which move randomly between the atoms or molecules.

8.3 Convection
Convection is the transfer of thermal energy by means of currents in a fluid or gases.

When water at the bottom of a container is heated, it expands -> Expanded water is less dense and start to ride -> Cooler regions of the water in the upper part on container became denser and sinks.

Convection currents occur only in fluids such as liquids and gas but not in solids.
Because convection involves the bulk movement of the fluids which carry thermal energy with them.

8.4 Radiation
Radiation is the continual emission of infrared waves from the surface of all bodies, transmitted without the aid of a medium.
The process in which energy is emitted as particles or waves.

Radiation can take place in a vacuum.

Factors affecting rate if infrared radiation

1. Colour and texture of the surface
2. Surface temperature
3. Surface area

Absorption = take in
Emission = give out

Best absorption and emission: dull black surface

Physics: Chapter 7 - Kinetic Model of Matter

Matter are tiny particles which are always in continuous, random motion.

Solid

• Closely packed atoms or molecules
• Strong intermolecular bonds
• Atoms or molecules vibrate about fixed positions.

Liquid

• Atoms or molecules occur in clusters
• Slightly further apart compared to solids
• Free to move about between clusters

Gas

• Atoms or molecules are very far apart
• Negligible attractive forces between atoms or molecules
• High speed, independent motion in random manner

Brownian motion
Gas particles move faster at higher temperature due to a increase of thermal energy which is converted to kinetic energy of the air molecules.

Physics: Chapter 6 - Energy, Work and Power

6.1 Energy
Energy is the capacity to do work.
SI Unit: joule (J)

Types of energy:

1. Kinetic Energy
   
2. Potential Energy (Chemical potential, elastic potential and gravitational potential)

1. Kinetic Energy
Moving objects have kinetic energy.

2a. Potential Energy - Chemical Potential Energy
Can be found in food, fossil fuels.

2b. Potential Energy - Elastic Potential Energy
A spring or rubber band possesses elastic potential energy when compressed or stretched.
When released, it is converted into kinetic energy.

2c. Potential Energy - Gravitational Potential Energy
The higher the object that leaves the ground, the greater the gravitational potential energy.

Principle of Conservation of Energy

Energy can neither be created nor destroyed in any process. It can be converted from one form to another or transferred from one body to another, but the total amount remains constant.

Conversion of energy
Efficiency = useful energy output divide energy input times 100%

6.2 Work

Work done by a constant force on an object is given by the product of the force and the distance moved by the object in the direction of the force.

W=F(s)
Work done by a constant force = constant force(distance moved by the object in the direction of the force)

One joule is defined as the work done by a force of one newton which moves an object through a distance of one metre in the direction of the force.

No work is done when:

1. The direction of the applied force and the direction in which the object moves are perpendicular to each other, and
2. The force is applied on the object but the object does not move.

Mechanical Energy

1. Kinetic energy and work done
2. Gravitational potential energy and work done

1. Kinetic energy and work done
Kinetic energy = 1/2(mass of body)(speed of body)²

2. Gravitational potential energy and work done
Ep = mgh
Potential energy = mass(gravitational field strength)(height)

6.3 Power
P= W/t = E/t
Power = work done over time = energy converted over time
SI Unit: watt (W)

One watt is defined as the rate of working or energy conversion of one joule per second

Physics: Chapter 5 - Turning Effect of Forces

5.1 Moments
The moment of a force is the product of the force and the perpendicular distance from the pivot to the line of action of the force.

Moment of a force = Fxd
Force(perpendicular distance from pivot) = Moments

Moment = turning effect of force

5.2 Principle of Moments
When a body is in equilibrium, the sum of clockwise moments about a pivot is equal to the sum of anticlockwise moments about the same pivot.

An object is said to satisfy the Principle of Moments when the force acting in clockwise motion is the same as force acting in anticlockwise motion on the same pivot.

Conditions for equilibrium:

1. All forces acting on it are balanced (Resultant force is 0)
2. The resultant moment about the pivot is 0 (Principle of Moments must apply)
   

5.3 Centre of Gravity

The centre of gravity of an object is defined as the point through which its whole weight appears to act for any orientation of the object.

The centre of gravity of a body is a single point through which its entire weight acts.

5.4 Stability
Stability refers to the ability of an object to return to its original position after it has been tilted slightly.

Three cases of equilibrium:

1. Stable equilibrium
2. Unstable equilibrium
3. Neutral equilibrium

To increase stability of an object:

1. The centre of gravity should be as low as possible
2. The area of a base should be as wide as possible

Physics: Chapter 4 - Mass, Weight and Density

4.1 Mass and Weight
Mass is a measure of the amount of matter or substance in a body.
SI Unit: kilogram (kg)

Weight is a force and has direction.
SI Unit: newton (N)
Also know as gravity.

W = mg
Weight = mass(gravitational field strength)
Earth = 10kg^-1

4.2 Inertia
Inertia of an object refers to the reluctance of the object to change its state of rest or motion.

4.3 Density
The density of a substance is defined as its mass per unit volume.
p = m/v
Density = mass/ volume
SI Unit: kilogram per cubic metre (kg m^-3)

Physics: Chapter 3 - Forces and Pressure

3.1 Forces

A force is a push or a pull that one object exerts on another.
It produces or tends to produce motion, and stops or tends to stop motion.

SI Unit: newton (N)

3.2 Scalars and Vectors
Scalar quantities are physical quantities that have magnitude only
Vector quantities, however, are physical quantities that possess both magnitude and direction.

3.3 Forces and Motion
A force can cause:

1. A stationary object to start moving
2. A moving object to increase speed
3. A moving object to decrease speed
4. A moving object to change its direction of motion

Forces and Zero acceleration

For an object with zero acceleration, the different forces acting on it are balanced or add up to zero.

Balanced forces and Newton's First Law

Every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it to change its state.

Unbalanced forces and Newton's Second Law

When a resultant force acts on an object of constant mass, the object will accelerate and move in the direction of the resultant force.
The product of the mass and acceleration of the object is equal to the resultant force.

F = ma
Force = mass(acceleration)

SI Unit: Newton (N)

Weight is a force
W = mg

Newton's Third Law

For every action, there is an equal and opposite reaction, and these forces act on mutually opposite bodies.

3.4 Friction and its Effects
Friction always opposes motion between two surface in contact.

3.5 Pressure
Pressure = force / area
P = F/ A
SI Unit: newton per square metre (N m^-2)

Physics: Chapter 2 - Kinematics

2.1 Distance, Time and Speed
Speed = Distance moved / time taken
v = d/t

Average speed = total distance travelled / total time taken

2.2 Speed, Velocity and Acceleration
Acceleration = change in velocity / time taken

2.3 Speed- Time graphs
Area under the speed time graph gives the distance moved.

2.4 Acceleration of free fall
Acceleration due to free fall (acceleration due to gravity) does not depend on the material, size or shape.