Physical Science Review Ch. 5

Kinetic Energy

(Kinetic Energy, joules) Ek = 1/2 m (mass) v (speed)

Remember

1 JOULE = 1 N-m 1 Watt = 1 N-m/sec

How much work have you done if you drag a box with a force of 100 newtons for 10 meters and it takes you 10 seconds?

1,000 joules of work (If a friend does the same work but it takes 60 seconds, you do the same amount of work because the force & distance are the same BUT you did it in 10 seconds and it took them 6 TIMES LONGER.)

What happens in an very EFFICIENT machine?

All or most of the work INPUT becomes work OUTPUT.

What is the most efficient machine ever invented for turning the work of HUMAN muscles into motion?

BICYCLE It's efficiency is 95%.

Why is energy measured in joules like work is?

Because energy is really stored work. Any object with energy has the ability to use its energy to do work.

Nuclear Energy

Comes from SPLITTING AN ATOM or fusing 2 atoms together. Used to generate or make electricity in power plants. Used in medicine to treat cancer & other diseases.

What is Potential Energy?

Comes from the position of an object RELATIVE TO THE EARTH. (Marble lifted off the table, Earth's gravity pulls the marble DOWN, we apply force to lift it up. Applying force over a distance requires work, which gets stored as potential energy of the marble.)

Why is it correct to say ENERGY is CONSERVED in a machine?

Energy is conserved locally (ie, it can move but can't jump around) everywhere in the universe. That includes your machine. Your machine may "waste" energy by turning some of it into heat, but you can't actually destroy or create energy.

What is Kinetic Energy?

Energy of motion. (Basket at rest = no kinetic energy, apply force can give basket speed & kinetic energy. Applying more force increases speed & kinetic energy. Increasing mass increases kinetic energy because it takes more force.)

Mechanical Energy

Energy possessed by an object due to its MOTION or its stored energy of POSITION. Object that possesses this is able to DO WORK.

Example of energy transformation

Energy you use to climb a hill comes from food. The chemical potential energ is stored in the food you ate is converted into simple sugars. These sugars are burned as your muscles work agains the external forces (gravity) to climb the hill. In climbing the hill you convert some chemical energy to potential energy.

Thermal Energy

Heat is a form of thermal energy.

The FLOW of energy

In SKIING: Food (chemical energy) - height (potential energy) - speed (kinetic energy) - heat (thermal energy).

Where does "spent" energy go?

In climbing a hill, some energy goes to potential energy because you are up higher than where you started. Some energy is converted into heat, chemical changes in muscles and the evaporation of sweat by your skin.

Unit of measurement for work

JOULE (1 joule = to 1 newton of force X 1 meter of distance)

Radiant Energy

Known as ELECTROMAGNETIC ENERGY. (Light, x-rays, infrared radiation, radio waves, microwaves, etc.) Radiant heat from the sun keeps the Earth warm.

Block & Tackle machine lifts a load weighing 10 NEWTONS & you lift it 1/2 meter, how many joules of work on the load?

Machine has done 5 JOULES of work so the work OUTPUT is 5 JOULES.

What 2 things does kinetic energy depend on?

Mass & speed.

Law of Conservation of Energy

Nature NEVER CREATES OR DESTROYS energy. Only converted from one form or another. (input & output of machines an example of this)

Different forms of energy

Radiation, electrical, chemical & nuclear

Power

Rate at which work is DONE. Determine the amount of POWER OF A MACHINE by DIVIDING the amount of WORK DONE by the TIME it takes in SECONDS. P= W (work or joules)/T (Time or seconds)

Chemical Energy

Stored in molecules. Example is a battery. Chemical energy stored in batteries changes to electrical when connected to wires and a light bulb.

What is the EFFICIENCY of a machine?

The RATIO OF WORK OUTPUT TO WORK INPUT. Friction LOWERS efficiency. (To calculate it divide the work OUTPUT by the work INPUT)

What is the unit of power called?

The WATT named after James Watt, inventor of the steam engine.

Energy

The ability TO DO WORK. Anything with ENERGY CAN PRODUCE A FORCE that is capable of acting OVER A DISTANCE. Fundamental building blocks of our universe. Appears in different forms = motion, heat, matter, light, electricity, position, sound.

One JOULE of work = 1 newton-meter

The work OUTPUT of a simple machine can NEVER EXCEED the work INPUT! (You can never get more work out of a machine than you put into it! When you design a machine that MULTIPLIES force, you pay by having to apply the force over a greater DISTANCE.)

Horsepower

Unit of Power. 1 horsepower = 746 watts.

Work

WORK IS FORCE TIMES DISTANCE (W=FD) If you push a box with a force of 1 NEWTON for a distance of 1 meter, you've done 1 JOULE of work.

Electrical Energy

We use in our daily lives (appliances we plug in). Derived from other sources of energy.

Solar Power

When we harness the RADIANT ENERGY from the sun.

Energy Transformation

When you throw a ball in the air, its energy transforms from KINETIC to POTENTIAL and back to KINETIC.

Explain the relationship between WORK & ENERGY.

You must have energy to perform work - you don't necessarily perform work if you have energy. Potential energy is not work, kinetic energy is work.