AY Honors/Physics/Answer Key

1. Define the following:

a. Physics

A branch of science that deals with matter, energy, motion, charge, and force.

Physics uses a number of tools such as a balance, meter or ruler, clock or stop watch. Physicist also use more complicated tools as they look at more complicated events. The most important tool of physics is mathematics. You can think of Mathematis as the language of physics.

b. Mass

A quantity of matter related to weight by Newton's second law of motion represented mathematically as [math]\displaystyle{ F=m \times A }[/math]

c. Work

A measure of energy. If we push a heavy load, then the work that we do is how hard we push the load times how far we push the load.

[math]\displaystyle{ Work=Force \times distance }[/math]

d. Force

An influence on an object that causes the object to move or change direction.

e. Power

How much energy expended per unit of time. If you can do lots of work quickly, then you are using more power.

[math]\displaystyle{ Power= \frac{(Work\ done)}{(time\ it\ took\ to\ do\ the\ work)} }[/math]

f. Potential energy

The energy of an object based on its relation to other objects. For example if I lift a ball above the ground by a given distance, then the ball has the potential to fall the distance that I've raised it. The potential energy of a ball can be measured by measuring how high you raise the ball against the force of gravity on the mass of the ball.

Potential energy of the ball (E) = Mass of ball (m) * Accelleration of gravity (g) * height we rase the ball (h)

We write this [math]\displaystyle{ E=mgh }[/math]

g is the acceleration of gravity and is 9.8 m/sec/sec or 32 feet/sec/sec

g. Kinetic energy

The amount of energy that an object has based on its motion relative to other objects. Kinetic energy in it's simplest form is related to the speed of an object in relation to the observer. Kinetic energy in it's most complex form can be heat

The kinetic energy of a moving ball can be measured by knowing 2 things about the object 1) The mass of the object. (Determined using a scale.) 2) The velocity of the object (Time how long it takes to travel a given distance)

[math]\displaystyle{ Kinetic\ energy = 0.5 \times (Mass\ of\ object) \times (Velocity\ of\ object)^2 }[/math]

h. Weight

The force that gravity exerts upon a body. According to Newtons second Law of motion:

[math]\displaystyle{ The\ weight = (mass\ of\ object) \times (local\ acceleration\ of\ gravity) }[/math]

Weight is commonly mistaken for mass, but weight could be significantly more on a planet with larger gravity, or could be significantly less on a planet with a lower gravity. Mass on the other hand is the same in both circomstances.

i. Matter

Something that has mass. There are four states of matter: solid, liquid, gas, and plasma.

j. Inertia

A property of matter that works against an external force. According to Newton's first law of motion, a body at rest tends to stay at rest unless acted on by an outside force. An object in motion tends to stay in motion unless acted on by a force.

k. Friction

The rubbing of surface one object against the surface of another.

At the atomic level you can think of bumpy surface like sand paper rubbing against another surface. When the two surfaces are at rest, the high spots of one surface fit into the valleys of the other surface and it takes quite a bit of force to move one over the other. Once they are moving, the two surfaces bounce from peak to peak like a skiier only hitting the tops of the moguls.

l. Wave

A disturbance traveling through a medium by which energy is transferred from one particle of the medium to another without causing any permanent displacement of the medium itself.

In a guitar string for example, the string will vibrate up and down, but the particles that form the string do not move horizonally along the string. Likewise, if you throw a pebble into the water, the water goes up and down and the wave spreads out from the splash point, but there is not a flow of liquid along the surface of the water.

m. Center of gravity

The point from which all the gravitational forces within an object appear to come. This point is the same as the center of mass in a uniform gravitational field.

n. Exponential notation

Scientific notation is a mathematical notation that makes it easier to work with very large numbers or with very small numbers. In physics it is very common to have very large numbers such as the number of atoms in a drop of water, or the number of stars in a galaxy. It is also quite possible to have very small numbers such Planck's constant.

We write numbers in scientific notation by getting rid of the zero space holders.

In large numbers

[math]\displaystyle{ 1X10^9 }[/math]=1,000,000,000

[math]\displaystyle{ 6.02X10^{23} }[/math]- 602,000,000,000,000,000,000,000

[math]\displaystyle{ 2.9979^8=299,790,000 }[/math]

For small numbers the exponent is negative

0.00001= [math]\displaystyle{ 1X10^5 }[/math]

0.000000015=[math]\displaystyle{ 1.5X10^8 }[/math]

The exponent tells us how many places we need to move the decimal point. We move it to the right for positive exponents and we move it to the left for negative exponents.

Exponential notation is used on many calculators and programming laguages. the X10 is replaced by the letter E

We would write [math]\displaystyle{ 31E6 }[/math] instead of [math]\displaystyle{ 31X10^6 }[/math].

o. Absolute zero

A theoretical minimum temperature at which all motion of an atom ceases.

This minimum temperature is:

0° Kelvin= -273° Centegrade = –459.67° Fahrenheit

p. Fulcrum

The support, on which a lever turns in moving a body.

The Center support of a teeter totter is the fulcrum.

About the Author

--Rodneyeast 14:06, 23 October 2006 (UTC)