Physics exam 2

Why are damns thicker at the bottom?

• In order to withstand the greater force exerted by the water against the lower portion of the structure

• The pressure exerted by water increases with depth

Buoyancy

• The upward force exerted by fluid on an object

• Force= weight of the fluid displaced by the object and acts in opposite direction to gravity

How much weight does a floating boat displace?

• Displaces the amount of water equal to its weight

Does the density of liquid matter (salt vs. fresh water)?

YESS!

• Salt water is denser than freshwater

Submerged objects displaced their volume

It is displaces a volume of fluid equal to its volume

How is buoyancy affected if an object is only partly submerged?

Buoyant force acting on it is equal to the weight of the fluid displaced by the submerged portion of an object

Temperature scales

• 0 K and -273.15 C represent the absolute zero

• -273.15 C = 0 K

Temperature - measure of average molecular translational kinetic energy

• Measure of the average kinetic energy of molecules in substance. Quantifies how fast particles move within a material

• Temp. increases, the average kinetic energy of particles increase leading to rapid molecular motion

High specific heat

slow release of energy

Specific heat

the amount of heat required to raise the temp

Example of high specific heat

Large bodies of water with high specific heat can absorb and store heat during the day and release it at night, moderating costal temperatures

Why does heat cause expansion

• Molecules absorb energy and vibrate more rapidly

• Causes molecules to push against each other and move further apart, leading to expansion of substances

Why is ice less dense then liquid water?

Because of crystalline structure

Why are metals good conductors of heat and electricity?

• Due to the presence of free electrons these electrons can move easily, carrying energy with them

• Atoms not strongly bound

Conduction

Transfer of heat through direct contact transferred from higher temperature regions to lower

Convection

Transfer of heat through the movement of fluid

Radiation

Transfer of heat through electromagnetic waves

What is a fluid

Both liquids and gases

Relationship between reflection and absorption in a material

• Good reflectors tend to be poor absorbers

• The reflection and absorption of light or electromagnetic radiation by a material are inversely related

What do the 1st law of thermodynamics and the law of conservation energy have in common?

Energy cannot be created nor destroyed

All mechanical work causes heat

When mechanical work is performed on an object or by an object some of the energy is converted into heat due to inefficiency in the process

What is the maximum efficiency of a machine?

100%

What is wasted?

Heat

What is entropy?

• Measure of the disorder or randomness of a system

• Amount of energy in a system that is not available to do work

What is a wave?

Disturbance that travels through medium or space

What is a waves source?

Vibrating objects

Electromagnetic wave

Oscillating electric and magnetic field travel in a vacuum

Ex: Light, radio, microwaves

Mechanical wave

Sound and water require medium vibration of particles

What do waves transport

Energy

Wavelength

Distance between 2 consecutive points

Frequency

Number of oscillations or cycles it completes per unit of time (Hz)

Speed

Rate at which traveled through medium (wavelength and frequency)

Constructive

Crest of 2 waves align resulting in wave with greater amplitude

Destructive

• Crest of one wave aligns with the through of another wave

• Wave with reduced amplitude=complete cancellation

Wave interference

Two or more waves inter lapping in space

What makes electrons move?

• A potential difference (voltage)

• Potential difference created electric field within a conductor

Voltage

• Does not flow like current does

• Measurement of potential energy difference

• Two points in a circuit

Resistance

• Does not flow either

  • How much it resists the flow of current

Current

• Flow of electric charge (usually electrons)

• In response to a voltage

Where do electrons that power machines come from?

• Electrons come from the flow of charge within a circuit

• Sourced from atoms in conductive materials

• Movement of ions

How fast do electrons flow in a circuit?

More relatively slowly

How does the thickness of a wire or pipe affect resistance?

Thicker wires or pipes have lower resistance

The electromagnetic spectrum

All forms of electromagnetic radiation

• Radio waves

• Microwaves

• Infrared radiation

• Visible light

• UV radiation

• Xrays

• Gamma rays

Visible light

• Small portions of electromagnetic spectrum that is visible to the human eye

• Sensation of sight composed of different colors each corresponding to a specific wavelength

How does light get through glass? Does the frequency change?

• Glass is transparent to visible light

• Transmitted through it, absorbed by it, or reflected by its surface

• Frequency of light does not change, decreases slightly due to interactions with the material

Incandescent bulbs

• Work by passing an electric current through a thin filament which heats up and produces light due to its high temperature

• Inefficient because they convert a significant portion of electrical energy into heat rather than light

• Shorter life span

Fluorescent bulbs

• Contain gas and a small amount of mercury vapor

• More energy efficient than incandescent bulbs and produce less heat for the same amount of same amount of light output

• Contains hazardous materials

LED bulbs

• Passing an electric current through a semiconductor material

• Highly energy efficient, converting a higher percentage of electrical energy into light and producing heat

• Longer lifespan and more durable

How does energy flow?

Energy always flows from high to low

Coherence laser

• Electromagnetic waves have the same frequency and phase

• Interferes constructively and produces a highly focused beam

Monochromaticity laser

Monochromatic and consists of a single wavelength or color

Directonality laser

• Highly directional

• Travels in a narrow beam with minimal divergence

• Concentrated energy over long distances

• Ex: laser cutting, laser surgery, & laser ranging

Energy output in a laser

Intensity of the laser beam

Energy input in a laser

Electricity or pump energy supplied to the laser