Assessment for this course Final exam: 60% Mid-semester exam: 20% Quiz x 3: 10% Homework: 10% If you do the homework, the rest should be easy!

Assessment for this course

• Final exam: 60%• Mid-semester exam: 20%• Quiz x 3: 10%• Homework: 10%

If you do the homework, the rest should be easy!

Homework

After every lecture, I will suggest a few problems for you to try.

Make sure you can do them!

How?• Read the textbook• Ask your friends• Ask me (Thursday or Friday, not on the weekend!).

HomeworkStarting from week 3:

The first lecture of each week (Monday morning), I will explain some of the problems from the previous week.

Then, I will choose one of the problems for you to do. (Probably an easy one.)

You will write the solution, and hand it to me at the end of that lecture period.

In this course, we will learn about four

fundamental principles.

(1) Momentum principle动量原理

(2) Energy principle 能原理(3) Angular momentum principle 角动量原理(4) Fields 场

The principles of physics help us understand

matter and its interactions.

相互作用

How do we detect interactions?

检测

Blackboard

1. Change in direction2. Change in speed3. Change of shape4. Change of phase5. Change of temperature6. Change of identity

Interactions cause change.

We focus on these two.

Change in direction

Change in speed

Change in velocity means: Change in direction, or speed, or both. 速度

Uniform motion is motion with a

constant speed and a constant direction.

In other words, a constant velocity.

Uniform motion implies no net

interaction.

This is not obvious!

Aristotle亚里士多德

(384 BC – 322 BC)He believed that the natural state of an object is to be motionless; any motion must be caused by a force.

His ideas were accepted for 2000 years.

Galileo伽利略

(1564– 1642)

Showed that, in the absence of friction, or other forces, an object will keep moving forever. 摩擦力

Isaac Newton牛顿

(1643 – 1727)“Isaac Newton was born on Christmas day, 1642, within a year of Galileo’s death. Newton was a short man, nearsighted, already silver-gray in his thirties, inattentive to personal appearance, incredibly forgetful, and probably forever virginal. This nervous, hypochondriacal, sensitive, pious, vulnerable man was one of the greatest geniuses to ever live. Among Newton’s many achievements was a theory of motion that withstood every test for over 200 years.”

- E. Hecht, Physics: Calculus, chap 4

Newton’s First Law of Motion

An object moves in a straight line and at constant speed, except to the extent that it interacts with other objects.

Newton’s First Law of Motion

任何物体都要保持其静止或匀速直线运动状态，直到外力迫使它改变运动状态为止。

Which of these particles did not interact with something?

(1)A(2)B(3)C(4)D (5)A and B