Announcements Midterm-I is on Thursday (Feb. 10th) between 5:30-6:30 pm.

Topics included are Chapters 1, 2, and 3 STUDY GUIDE is available in the course home page at

http://physics.okstate.edu/babu/2014 A formula sheet will provided to you during the test. For further

details see the study guide Those who don’t have access to web can download the study

guide from library or can come by during the office hours to pickup a copy

All HW solutions should be available on the web for you to study them for the test

HW4: (Chapter 4): 4, 6, 9, 12, 28, and 34 (a, b, c) Due: Feb 18th. There would not be regular class meeting on the exam day

(02/10/05) but, I will review the exam material. Those interested may attend

Chapter 4 (contd.) : Newton’s Laws In the light of various types of forces, we will

attempt to address the following questions• What does a Force do? – A virtual experiment• How does an object move when an external force

is applied? • Are there additional relationships between Force

and motion? – Newton’s Laws• What is the “natural state” of an object? – the

beginning of physics! Mass – definition of Free body diagrams

What do forces do?

Stretching of N rubber bands require a net force of NF

Effect of Force – A virtual experiment

Pull the block of mass with different F values and note down a

Plot F versus a Observer that F is

proportional to a Slope of the graph is a

constant Observation: a F

Does the acceleration depend on the size of an object?

Plot dependence of a for different values of F

Observe that the slope of the graph changes with size of the object

If size of the object is proportional to the matter it contains, slope is inversely proportional to the size of the object

Loosely speaking, the size of the matter is defined as “mass” of the object

Mass 1/C and C (a/F)

Stop to Think What do you mean by the size of the object? What is the relationship between the slope of F

versus a graph? Does the slope depend on the size of an

object? Is there a better way of describing the size of

an object? Is the shape of an object relevant? Can we put both size and shape into a single

entity?

Newton’s Second Law

An object of mass “m” subjected by a net force F experiences an acceleration a in the direction of the net Force F

~a =~F n etm

Basic unit of Force is Newton and is denoted by N 1N = 1kg x 1m/s2

1lb weight = 4.45 N

Example

Two forces (T1,T2) are acting on an object of mass “m”

The direction of net force can be obtained by applying the parallogram theorem

Free body diagram (FBD)