Physics 203 – College Physics I Department of Physics – The Citadel

Physics 203 College Physics I Fall 2012

S. A. Yost

Ch. 1 – Ch. 2

Introduction – Part 2 Motion in 1 Dimension – Part 1

Physics 203 – College Physics I Department of Physics – The Citadel

College Physics I

I am Professor Yost .

Office: Grimsley 246 upstairs near your labs.

Hours: Mon. 2 – 5 PM, Tu, Th. 9:15 – 11 AM or by arrangement (not Friday, generally) Textbook: Douglas Giancoli, Physics, 6 th Ed .

(Chapters 1 – 12) The new textbooks in the Citadel book store are packaged with a MasteringPhysics access packet. You also need an i>clicker .

Physics 203 – College Physics I Department of Physics – The Citadel

Today’s Topics & Announcements

1.

Units, Scientific Notation, Significant Digits 2.

Graphs – Mathematical Review 3.

Introduction to 1 Dimensional Motion Due to a change of policy, all labs are meeting this week , although sections11 and higher will not be doing an experiment, just introductory material.

If you missed one yesterday, you should not have been marked absent, but may wish to contact your instructor for a copy of the syllabus.

Physics 203 – College Physics I Department of Physics – The Citadel

Thursday’s Assignment

Read Chapter 2 through section 5 . A quiz on these sections using i>clickers should be anticipated.

You “read” physics by working the examples and convincing yourself that all statements are true.

Complete Problem Set HW1 on MasteringPhysics .

HW1 is mostly on Chapter 1 , with a couple of mathematical review tutorials on graphing, which should be helpful in reading Chapter 2 .

Physics 203 – College Physics I Department of Physics – The Citadel

Citadel Physics Department

High energy physics: Drs. Yost, Berlinghieri Space physics: Drs. Sollitt and Briggs Astrophysics: Dr. Adelman Condensed matter: Drs. Hilleke and Clark Quantum Foundations: Dr. Gomez

Physics 203 – College Physics I Department of Physics – The Citadel

High Energy Physics

I calculate processes observed at the Large Hadron Collider at CERN, the highest-energy particle collider in the world, which attempts to see what particles lie beyond those that could be produced in the past, and probe the physics that ruled the universe in the first microseconds of the Big Bang.

Physics 203 – College Physics I Department of Physics – The Citadel

ATLAS ALICE CMS LHCb

Physics 203 – College Physics I Department of Physics – The Citadel

Condensed Matter

A lot of recent work has focused on ultra-cold atoms and manipulating individual atoms at very short distances. Applications include nanofabrication of materials at the atomic level and building “quantum computers”, which may allow calculations beyond the reach of current computers. Dr. Clark works in these areas.

Physics 203 – College Physics I Department of Physics – The Citadel

Space Physics

Dr. Sollitt participated in the LCROSS mission to seek water on mars by crashing a spacecraft into a crater.

He is also interested in Mars exploration and exobiology. Physics majors participate in high altitude balloon experiments and other activities…

Physics 203 – College Physics I Department of Physics – The Citadel

Citadel Cadets: Suborbital Training

Physics 203 – College Physics I Department of Physics – The Citadel

What’s Wrong With This Picture?

Physics 203 – College Physics I Department of Physics – The Citadel

What’s Wrong With This Picture?

How do you add a time, a distance, and a number of people?

Physics 203 – College Physics I Department of Physics – The Citadel

Units

In physics, numbers have

units

being measured. that show what is Giving a number without showing the units is meaningless. Numbers with different units cannot be added: What is a year + a mile? Nonsense Numbers with different units can be multiplied or divided. The result has velocity… composite units . For example, a distance divided by a time is a 20 m / 5.0 s =

4.0 m/s

Physics 203 – College Physics I Department of Physics – The Citadel

SI Units

What are the three basic units of mechanics?

Kilograms, Meters, Seconds

All other units we will use are derived from these. We’ll need another basic unit when we get to electricity and magnetism: the Ampere, which measures electric current.

Physics 203 – College Physics I Department of Physics – The Citadel

Radius of the Earth

Suppose you need to know the radius of the earth but don’t have a way to look it up.

If you remember the original definition of the meter, you can figure it out.

How?

Physics 203 – College Physics I Department of Physics – The Citadel

Radius of the Earth

The distance from the equator to the north pole was defined to be 10,000 km .

40,000 km = 2 p R R = 6367 km Book says: 6380 km R

Physics 203 – College Physics I Department of Physics – The Citadel

Unit Conversions

If a car goes 25 m/s , what is its speed in miles per hour?

Given: 1 km = 0.62 mi, 1 hour = 3600 s.

Then 1 m = 0.62 x 10 -3 mi Multiply by conversion factors to cancel the unwanted units, given the wanted ones.

Physics 203 – College Physics I Department of Physics – The Citadel

Unit Conversions

Multiply 25 m/s by 1 = 0.62 × 10 -3 mi / 1 m 1 = 3600 s / 1 h 25 m/s = 25 m/s (0.62 × 10 -3 mi/m) (3600 s/h) The unwanted units cancel. = 56 mi/hr

Physics 203 – College Physics I Department of Physics – The Citadel

Nautical Miles

A nautical mile is one arc-minute of latitude on the Earth. How many km are in a nautical mile ?

There are 90 degrees of latitude between the equator and pole. Each degree has 60 arc-min .

So there are 5400 nautical miles from the equator to the pole, which is 10,000 km .

1 nmi x = 1.852 km 5400 nmi (exactly)

Physics 203 – College Physics I Department of Physics – The Citadel

Significant Digits

Suppose I am measuring the speed of a car, and have a well measured length of 100.00 m . If I find that the car’s time to cross this distance is 4.0 s , what is its speed?

The car’s speed is v = 100.00 m / 4.0 s = 25 m/s.

The result is quoted to 2 significant digits, because that is the time is the limiting factor in the precision.

Physics 203 – College Physics I Department of Physics – The Citadel

Significant Digits

Significant digits are ones that can be known based on the measurements.

1.25

3 significant digits 1.20

125 3 significant digits 3 significant digits 120 maybe 3, but maybe only 2 A common convention to show that the 0 in 120 is significant is to put a decimal point at the end: 120. (3 sig. fig.) vs 120 (2 sig. fig.), but this is not universally used, so it is still ambiguous.

Physics 203 – College Physics I Department of Physics – The Citadel

Scientific Notation

Scientific Notation is more precise: 1.2 × 10 2 has 2 significant digits 1.20 × 10 2 has 3 significant digits.

All displayed digits are significant in scientific notation: no “place holders” such as the zero in 120 are needed.

Physics 203 – College Physics I Department of Physics – The Citadel

Example

What is the mass, in kg, of a cubic foot of water?

1 in = 2.54 cm and the mass of 1 cm 3 of water is 1 g .

1 ft = 12 in = 30.48 cm 1 ft 3 = (30.48 cm) 3 = 28.3x10

3 cm 3 10 3 cm 3 of water has a mass of 1 kg .

1ft 3 of water has a mass of 28.3 kg .

Physics 203 – College Physics I Department of Physics – The Citadel

Order of Magnitude Estimates

The order of magnitude of a number is the nearest power of 10. (1 L = 1000 cm 3 ) Estimate the number of liters of water on Earth.

The Earth’s radius is about 6000 km (to 1 sig. fig.) Its surface area is mostly ocean: A = 4 p R 2 = 12 × 36 × 10 6 km 2 ≈ 4 × 10 8 km 2 The average ocean depth is probably a few km, so V ≈10 9 km 3 = 10 9 (10 5 cm) 3 = 10 24 cm 3 = 10 21 L

Physics 203 – College Physics I Department of Physics – The Citadel

Kinematics

We will begin with the study of kinematics: the description of motion, without regard to its cause.

It takes two locations to describe the motion of an object: the location of the object moving, and the location of the observer. The location of the object is always given relative to the observer, which may be moving as well.

From the sun’s point of view, the earth orbits around it. From the earth’s point of view, the opposite is true.

Physics 203 – College Physics I Department of Physics – The Citadel

Position-Time Graphs

This graph shows the position of an object as a function of time.

We will use such graphs frequently to represent motion.

What is the position of the object at t = 6 s ?

x = 2 m 2 1 4 3 x (m) 0 1 2 3 4 5 6 7 -1 t (s) -2 -3

Physics 203 – College Physics I Department of Physics – The Citadel

Displacement

The change in position is called displacement .

What is the displacement from t = 0 to t = 6 s ?

D x = 4 m 4 3 x (m) 2 1 D x 0 1 2 3 4 5 6 7 -1 t (s) -2 -3

Physics 203 – College Physics I Department of Physics – The Citadel

Average Velocity

The displacement divided by 4 the time is the average 3 velocity .

2 x (m) What is the average velocity 1 between 0.0

and 6.0 seconds?

D x D t 4.0 m 6.0 s -1 -2 0 1 2 3 4 5 6 7 D t D x A straight line depicts motion -3 at constant velocity . The velocity is the slope .

t (s)