Science exam chapter 7

7.1

Energy:

Energy is the ability to do work

Work

The amount of energy transferred when a force causes an object to move some distance.

Measured in joules (j)

Calculating work:

Work= net force x displacement

W=FS

W is work, measured in joules (j), F is the next force acting on the object measured in netwons (N), s is the displacement ( distance from the origin point, in the direction of the force) measured in metres.

Kinetic energy

The energy an object or particle has due to its motion.

Kinetic Energy formula: Ek=1/2mv

Ek is kinetic energy which is measured in joules (j),m is the mass of the object in motion measured in kilograms (kg), and v is the velocity at which the object is moving measured in metres per second (m/s or ms-1)

Potential energy:

The energy stored in an object due to the objects positioning in regards to other objects, its arrangement or its state.

Calculating Gravitational potential energy:

Formula: Ep=mgh

Ep is the gravitational potential energy measured in joules, m is the mass of the object measured in kilograms, g is the gravitational acceleration experienced by the object due to the strength of the Earths gravitational field (9.8ms-2), h is the height of the object above the surface of the Earth measured in metres (m).

Elastic potential energy:

The energy stored in an object due to its shape, usually resulting from the other object either being compressed or stretched.

Calculating Elastic potential energy:

Ee=1/2kx²

Ee is the elastic potential energy measured in joules, k is the elasticity constant which is an indication of the stiffness and is measured in newtons per metre, x is the linear length that it has been exanded by or compressed to measured in metres.

7.2

Law of onservation of energy:

Energy can be neither created or destroyed, only converted from one form of energy to another or transferred between objects.

Examples of transformation:

Fireworks: chemical energy→thermal, light, sound, kinetic

Toaster: electrical energy→Thermal

Energy efficiency:

Not all transformations are 100% efficient.

Useful energy: The output energy a device is designed to produce.

Wasted energy: Energy converted to unwanted forms (usually heat).

Input energy= Useful output energy + Wasted output energy

Eg: Light globe- only 10% of the input energy becomes light.

Energy efficiecny and calculating:

Energy efficiency is the percentage of input energy that is converted to useful energy by a machine or system.

Calculated using the formula: Efficiency (%)= useful output energy (j) / input energy (j) x 100

7.3

Sources of Energy:

Renewable: Can be replenished as fast or faster than it is used.

Non-Renewable: Cannot be replenished as fast or faster than it is used.

Fossil Fuel: Non-renewable energy sources such as oil, coal or natural gas that has formed underground from plant and animal remains over millions of years.

Sustainable: Practices that use natural resources responsibly, so they remain at the same level to support present and future generations.

Non-renewable energy: Coal

Coal is formed from ancient forests 300 million years ago. It is mined and burned to generate thermal energy, then electrical. It is typically 20-40% efficient. Issues is that they produces CO2 (greenhouse gases).

Non renewable energy: Nuclear

Radioactive substances (mainly uranium) are used as fuel. A small amount of fuel produces enormous energy. The electricity generation results in no direct greenhouse gas emmisions. Issues is that it causes radioactive waste.

Renewable energy: Wind

The kinetic energy of wind is converted to electrical energy. Free, non-polluting, and it is available at night. About 45% is efficient at converting wind to energy. Disadvantages: It depends on the winds availability.

Renewable energy: Solar

It converts light energy from sunlight direclty to electrical energy. It is free after the initial cost and is non-polluting. The solar panels are about 20% efficient and the labratory efficiencies are up to 47.5%. Disdvantages is that is depends on the weather and it does not work at night.

Renewable energy: Hydroelectric

Uses gravitational potential energy of water held in dams. Water flows through turbines to generate electricity. It accounts for about 7% of Victoria’s energy production. Disadvantages is that Dam construction, floods an area of land.

Renewable energy: Geothermal

Uses thermal energy from Earths interior. Water pumped into hot rocks creates steam. Disadvantages is that it has a limited number of viable locations.