This document provides an agenda and overview for a physics unit on friction, momentum, and work. It includes an introduction and definitions for each topic. There is also information about upcoming homework, labs, and course modules. The second part describes a lab simulation on forces and friction that students will complete, with step-by-step instructions and questions to answer.

1. Unit 2 Part 1
Friction
Momentum
Work
Lab 1
Dr. Paul H. Comitz
pcomitz@live.com

2. Agenda
 Friction
 Momentum
 Work
 HW 1 due tonight
 Unit 2 hw will be distributed next week
 Lab Manual #3 (labeled lab 2 on LMS)
 Summary
 As time allows
 Learning how to learn Study Tips

3. Course Modules
# Module Weeks Reading Quiz
1 Newton's laws 1 Ch 4,5 *
2 Conservation of Energy and
Momentum
2,3 Ch 6,7,8 Quiz 1
3 Thermodynamics 3,4 Ch 12,13,14
4 Electromagnetism 5,6 Ch 17,18 Quiz 2
5 Waves, Sound, and Light 7,8 Ch 16, 20, 21 Quiz 3
6 Modern Physics 9,10 Ch 23 Final Exam
* it is strongly recommended you read chapters 0 - 3

4. Module 1

5. Module 2

6. Review : Newton’s Laws of Motion
 Newton's First Law
 A body that is in motion continues in
motion with the same velocity (at
constant speed and in a straight line)
and a body at rest continues at rest
unless an unbalanced (outside) force
acts upon it.
 Newton’s Second Law
 The total force acting on a body is
equal to the mass of the body times its
acceleration.
 Newton’s Third Law
 For every action (force), there
is an equal and opposite
reaction (force)

7. Friction
 A force that resists relative motion between
two objects in contact
 “Caused by the irregularities of two surfaces
sliding or rolling across each other”

8. Static and Kinetic Friction
 Static – a force that opposes the start of
motion
 Kinetic – once the objects are in motion, the
friction is less, and is called kinetic friction

9. Friction
 Force acts parallel to surface in contact
 Opposite direction of motion
 Friction force increases as force between
surfaces increases
 Formula
 Ff = mFN
 m is the coefficient of friction

10. Coefficient of Friction : m
 Ratio between the friction force and the
normal force on an object
 m describes how smooth or how rough
surfaces are when they come into contact
with each other
 Low number smooth surfaces
 High number rough surfaces
Normal Force

11. What is Momentum ?
 A measurement of mass in motion
 How much mass is in how much motion
 Formula
 p = mv
 p is linear momentum
 m is mass
 v is velocity
 units : kg * m/s
 Momentum is a vector
 Magnitude and direction

12. Impulse
 Quantifies the effect of force acting over time
 Impulse is the change in momentum
 J = Dp
 How are impulse and momentum related ?
Gaddis 8th edition
chapter 6-1

13. Conservation of momentum
 If the net external force acting on a system of
objects is zero, the vector sum of the
momenta of the objects will remain constant
 Newton’s cradle
 See http://www.lhup.edu/~dsimanek/scenario/newton.htm

14. Work
 In Physics work means something different
than a task requiring physical or mental effort
 Work is done on an object when a force causes a
displacement of the object
 Work is the product of force in the direction of
displacement
 W = F*s (s is displacement)
 Work = Newton x meters = N * m
 1 N m = 1 joule (pronounced jewel)
 US Units : feet * pounds = foot pound

15. Examples
A person pulls a sled along level ground a distance of 15 m
by exerting a constant force of 215 N at an angle of
30 degrees. How much work is done?

16. Work done by a Constant Force
W = F d cos q
q
F
F cos q
d

17. Lab Manual # 3 Forces
(also labeled as Lab # 2)
 http://phet.colorado.edu/en/simulation/forces-1d
 Requires installation of Java Runtime Environment
 Ability to download an run jnlp (java network launch
protocol)
Click Download

18. Download and Launch the lab
 Double click the file: forces-1d_en.jar
 The lab will launch

19. Lab Part 1 Initial Setup
(see lab manual fig 3-6)
 Friction off
 Show Ffriction off
 Show FApplied off

20. Lab Step 1 Part 2
 Position 9.9 m
 Velocity increases to 4.4 m/s
 Acceleration increases as velocity changing, force
applied
Note: In the screen captures
That follow, you should your results
May be similar but they will not
be identical

21. Lab Step 3
 Acceleration versus time graph
 Force versus time graph

22. Lab Step 4
 Linear or parabolic ?

23. Lab Step 4b
 Newton's Second Law. "If the net force on an
object is not zero, the object will accelerate.
The direction of the acceleration is the same
as the direction of the net force. The
magnitude of the acceleration is
directly proportional to the net force
applied, and inversely proportional to the
mass of the object.

24. Lab Step 4c/d
 Use Rewind/Playback, hit pause at 3 s
 F= ma
 200kg * 2m/s2
 400 N
 Read Graph, get 395 N

25. Lab Part 1 Step 4e
 Screen shot of free body diagram

26. Lab Part 1 Steps 5-6
 Show FFriction , Show FApplied , Friction on,

27. Lab Part 1 Step 6

28. Lab Part 1 Step 7
 Acceleration versus Time
 Forces versus Time

29. Lab Part 1 Step 8
 A. linear or parabolic
 B. Order the forces from greatest to highest
 C. FTotal
 D. Acceleration

30. Lab Part 1 , Step 8e
 Rewind and playback to t = 3s

31. Lab Part 1 , Step 8e, f, g
 e) F = ma
 M = 200 kg, a = 0.7 m/s2
 F = 140N
 f) Read Graph
 g) Free Body Diagram

32. Part 2 and Questions
 For part 2 , select a different object and
perform the indicated steps
 Answer the question s
 Submit the Physics Lab Student Answer
Sheet
 Download from LMS