Physics

Topics of Physics• Mechanics – Motion and its causes• Thermodynamics – Heat and

Temperature• Waves – Repetitive Motion• Optics – Light• Electromagnetism – Electricity,

Magnetism and Light• Relativity – Moving Particles• Quantum Mechanics – Submicroscopic

Particles

ModelsA replica designed to show the structure or workings of an object, system, or concept.

A system consists of a single object and the items that immediately affect it.

Help build hypothesis and guide experimental design

UnitsAll measurements in physics MUST have a unit.1 m tells me an object is 1 meter in length.1 without a unit tells me nothing!

Units MUST agree!

Multiplying 1 cm x 1 m is not possible!1 cm = 100 m therefore 1 cm x 1m = 100 m x 1 m = 100 m

Metric Conversions

Base-10 system

Each prefix is 10 times larger or smaller than the next

king henry died by drinking chocolate milk

Scientific NotationSimple way to write really large or really small numbers

Large numbers have a positive exponent (numbers greater than 1)

Small numbers have a negative exponent (numbers between 0 and 1)

EquationsIndicate Relationships

Greek letter delta(change in)

Always rearrange the equation BEFORE plugging in numbers!

Equations

Solve the following equation for acceleration.

Dimensional Analysis• Units cancel• If you don’t have the units you want when you

are done then you did something wrong.

Dimensional AnalysisA billionaire offers to give you $5 billion if you will count out the amount in $1 bills or a lump sum of $5000. Which offer should you accept?

(Assume that you can count at an average rate of one bill per second, and be sure to allow for the fact that you need about 10 hours a day for eating and sleeping.)

Dimensional AnalysisTake the $5000!!!

It would take you 272 years to count out the $5 billion!

GraphsSummarize DataIndicate RelationshipsMake Inferences and Predictions

Graphs• Determine the slope of the line in each of the

following graphs.

1. 2.

Graphs1. 2.

Slope = 1.5 Slope = -1.5

Graphs

y = mx + bslope

y-intercept

GraphsIdentify the graph that matches each of the following stories:

1. I had just left home when I realized I had forgotten my books so I went back to pick them up.

2. Things went fine until I had a flat tire.

3. I started out calmly, but sped up when I realized I was going to be late.

Graphs

1. How many total miles did the car travel? 2. What was the average speed of the car for

the trip? 3. Describe the motion of the car between

hours 5 and 12? 4. What direction is represented by line CD? 5. How many miles were traveled in the first

two hours of the trip? 6. Which line represents the fastest speed?

Answer these questions about the graph on the right:

AnglesThings do not always move in a straight line

Understanding how to measure and use basic angles makes things easier.

Angles

Angles

If the baseline is 100 m and the angle at B is 60°, determine the distance from A to the tree.

AnglesTan B =

opposite

adjacent

Tan B =distance to object

baseline

(Tan B)(baseline) = distance to object

(Tan 60)(100 m) = distance to object

(1.73)(100 m) = distance to object

173 m = distance to object

Review• Models help us to understand how things work.

(Leads to hypotheses and experimental design)• Units are essential. No unit = No Credit!• Equations indicate relationships. (Always solve for the

variable before plugging in the numbers)• Dimensional analysis can weed out invalid equations.• Graphs allow us to make inferences and predictions.• Understanding angles makes it easier to solve

problems

Practice ProblemThe radius of the planet Saturn is 5.85 x 107 m, and its mass is 5.68 x 1026 kg.

a. Find the density of Saturn (its mass divided by its volume) in grams per cubic centimeter. (The volume of a sphere is given by )

Correct Answer – 0.677 g/cm3

b. Find the surface area of Saturn in square meters. (The surface area of a sphere is given by 4)

Correct Answer – 4.30 x 1016 m2

Practice ProblemAssuming biological substances are 90 percent water and the density of water is 1.0 x 103 kg/m3, estimate the masses (density multiplied by volume) of the following:

a. A spherical cell with a diameter of 1.0 µm (The volume of a sphere is given by )

Correct Answer – 5 x 10-16 kg

b. A fly, which can be approximated by a cylinder 4.0 mm long and 2.0 mm in diameter. (The volume of a cylinder is given by l)

Correct Answer – 1 x 10-5 kg