http://astro.temple.edu/~elenab/

What Is Physics?

Galileo Principle:-recognize that a scientific problem exists;

-state a hypothesis, an educated guess about the problem;

-predict the consequences of the hypothesis;

-perform experiments to see if the predictions occur;

-formulate the simplest general rule that organizes the hypothesis, predictions and experimental results into a theory.

Sir Isaac Newton under an apple tree…

Models of Atom

JJ Thomson:

PLUM PUDDING!

Models of Atom

Ernest Rutherford:

PLANETARY MODEL!

What is light?

Sir Isaac: PARTICLE!Huygens: No way! It’s a wave!

Albert Einstein and Max Planck:

Guys, guys! You BOTH are right!

Is the following hypothesis scientific?

(a) “The alignment of planets in the sky determines the best time for making decisions”

(b) “Intelligent life exists on other planets in the universe”

(c) “Life forms evolve from simple to more complex forms”

Which if these are scientific hypothesis?

(a) Atoms are the smallest particles of matter that exist.

(b) Space is permeated with an essence that is undetectable.

(c) Albert Einstein was the greatest physicist of the twentieth century.

Measurements

UNITS of SI system

For now we are interested in the base quantities of length, time, and mass. In the SI system (formerly known as the MKS system), their units are:

Quantity unit symbol

length meter m

time second s

mass kilogram kg

1 meter (abbreviated m) was originally chosen to be one ten-millionth of the distance from the Earth’s equator to either pole (1790).

1 second (s) was defined as 1/86400 of a mean solar day.

Power of Ten Notation

10

12

1020000000002.0

102000,000,000,000,2

Some Lengths or Distances

Proton radius 10-15 m

Atom 10-10 m

Football field length 102 m

Earth diameter 107 m

Earth to Sun 1011 m

Farthest galaxy visible 1026 m

Some Masses

Electron 10-30 kg

Proton 10-27 kg

Mosquito 10-5 kg

Person 102 kg

Earth 6x1024 kg

Sun 2x1030 kg

Galaxy 1041 kg

Some Typical Time Intervals

Lifetime of very unstable particle 10-23 s

Lifetime of muon 10-6 s

One day 10 5s

One year 3x10 7 s

Length of recorded history 10 11 s

Life on Earth 10 17 s

Age of Universe 10 18 s

Order of Magnitude

1. What are the criteria for accepting a theory as a physics law?

2. What role does the prestige of the scientist play in accepting a theory as a physical law?

3. What is the height of typical person, in centimeters? The length of typical newborn baby? The typical height of a bedroom ceiling?

4. What is the typical mass of 6-foot tall male, in kilograms? Of a 5-foot 6-inch tall female in kilograms?

SUMMARY

For a new idea to be accepted, it must (1) agree with the existing data; (2) make predictions that can be tested, and (3) have a scientific basis.

The measurement system used in science is the metric, SI system, based on meter, kilogram, and second.

The sizes of objects studied in physics range from entire Universe down to neutrons and protons.

Describing Motion:Kinematics in one dimension

Kinematics is a part of mechanics, which is the description of how objects move.

Translational

motion

Reference Frame

Speed

Speed is a measure of how fast object moves, measured by a unit of distance divided by a unit of time.

Instantaneous Speed

Average speed doesn’t indicate the different speeds that may have taken place during shorter time intervals.

Average Speed

average speed = total distance traveled/ time elapsed

Total distance traveled = average speed X time