Physics of Technology PHYS 1800 - PowerPoint PPT Presentation

Loading...

PPT – Physics of Technology PHYS 1800 PowerPoint presentation | free to download - id: 76b075-ZDZkN

The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Physics of Technology PHYS 1800

Description:

Physics of Technology PHYS 1800 Lecture 10 Review for Test 1 – PowerPoint PPT presentation

Number of Views:39
Avg rating:3.0/5.0
Slides: 23
Provided by: JRD80
Category:
User Comments (0)
Transcript and Presenter's Notes

Title: Physics of Technology PHYS 1800

1
Physics of TechnologyPHYS 1800
• Lecture 10
• Review for Test 1

2
PHYSICS OF TECHNOLOGY Spring 2009 Assignment
Sheet
Homework Handout
3
Physics of TechnologyPHYS 1800
• Lecture 8
• Mass Weight
• Motion with Friction

Introduction and Review
4
Notes on Test
1. Covers Chapters 1-4
2. 8 short answer problems or questions (5 point
each)
3. 3 Numerical problems based heavily on the
material from the homework and Lab/Demo sessions
(20 points each). One problem each from Chapters
2, 3 and 4.
4. You will have a formula sheet just like the one
in the handout.
5. Test is Thursday January 29 130-245 in ESLC 46.

5
What Do We Need To Measure?
• What is the minimum about things we need to know?
• Where things area length, L
• When things are therea time, T
• How thing interact with gravitya mass, M
• How things interact with EMa charge, Q
• How thing inter act with weak nuclear force
• How things interact with strong nuclear force

6
Scalars and Vectors
• Scalar Measure of quantity or size
• Sometimes called magnitude.
• Examples Length, volume, mass, temperature,
speed
• Vectors Many measurements in physics require a
knowledge of the magnitude and direction of
quantity.
• These are termed vector quantities.
• Examples Velocity, acceleration, force,
electric field
• Direction is an essential feature of a vector
quantity.
• Example Flying at 1000 km/hr due North is
quite different to the same speed due East!
• Vectors require 2 pieces of information MAGNITUDE
and DIRECTION.

7
Describing (Special) Motion
• Positionwhere you are in space (L-meter)
• Speedhow fast position is changing with time
(LT-1 or m/s)
• Accelerationhow fast speed is changing with time
(LT-2 or m/s2)
• We will focus on a special case of constant
acceleration due to gravity, termed FREE FALL.

8
Constant Acceleration
Acceleration ?
Distance ?
Speed ?
Time?
Time?
Time?
9
The Math Approach
• Lets put these ideas into math language

10
• Let the initial velocity be 20 m/s upward.
• It immediately starts experiencing a downward
acceleration due to gravity, of approximately 10
m/s.
• Every second, the velocity decreases by 10 m/s.
• After 2 s, the ball has reached its highest
point.
• Its velocity changes direction, from upward to
downward, passing through a value of 0 m/s.
• Now, the downward acceleration increases the
downward velocity.

11
Which of these three balls would hit the floor
first if all three left the tabletop at the same
time?
1. The ball with initial velocity v1.
2. The ball with initial velocity v2.
3. The ball with initial velocity v3.
4. They would all hit at the same time.

Since all three balls undergo the same downward
acceleration, and they all start with a vertical
velocity of zero, they would all fall the same
distance in the same time!
12
Projectile Motion
• Treating the vertical motion independently of the
horizontal motion, and then combining them to
find the trajectory, is the secret.
• A horizontal glide combines with a vertical
plunge to produce a graceful curve.
• The downward gravitational acceleration behaves
the same as for any falling object.
• There is no acceleration in the horizontal
direction if air resistance can be ignored.
• The projectile moves with constant horizontal
velocity while it is accelerating downward.

13
Dennisons Laws of Motion
1. Stuff happens (or not).
2. The bigger they are the harder they fall.
3. You get what you give.

14
Newtons Laws in Review
• 1st Law a special case of the 2nd Law for
statics, with a0 or Fnet0
• An objects velocity remains unchanged, unless a
force acts on the object.
• 2nd Law (and 1st Law)How motion of a object is
effected by a force.
• The acceleration of an object is directly
proportional to the magnitude of the imposed
force and inversely proportional to the mass of
the object. The acceleration is the same
direction as that of the imposed force.
• 3rd Law Forces come from interactions with other
objects.
• For every action (force), there is an equal but
opposite reaction (force).

15
Newtons First Law of Motion
An object remains at rest, or in uniform motion
in a straight line, unless it is compelled to
change by an externally imposed force.
16
Newtons Second Law of Motion
• Note that a force is proportional to an
objects acceleration, not its velocity.
• Precise definitions of some commonly used
terms
• The mass of an object is a quantity that tells
us how much resistance the object has to a change
in its motion.
• This resistance to a change in motion is called
inertia.

Force has dimensions of (MLT-2)
17
Net Forces
• It is the total force or net force that
determines an objects acceleration.
• If there is more than one vector acting on an
object, the forces are added together as vectors,
taking into account their directions.

18
Newtons Third Law (action/reaction)
For every action (force), there is an equal but
opposite reaction (force).
19
Mass, Weight, and Inertia
• A much larger force is required to produce the
same acceleration for the larger mass.
• Inertia is an objects resistance to a change
in its motion.
• Mass is a measure of an objects inertia.
• The units of mass are kilograms (kg).

20
Does a sky diver continue to accelerate?
• Air resistance R is a force directed upward, that
opposes the gravitational force W
• R increases as the sky divers velocity increases
• When R has increased to the magnitude of W, the
net force is zero so the acceleration is zero
• The velocity is then at its maximum value, the
terminal velocity

21
Free Body Diagrams
• Fancy Science Vector analysis of complex force
problems is facilitated by use of a free body
diagram.
• Common Sense A picture is worth a 100 words. (A
scale picture is worth an A!)
• Key is to
• Isolate a single body and draw all the forces
acting on it.
• Add up all the arrows (vectors).
• Whats left is the net force.
• Net force (and masses) ? a.
• A plus initial conditions? motion!

22
Example Sea Lion splash!
Fk
N
Fk
mg sin?
F
mg cos?
?
Free body diagram
Wmg
W m g
• Resolve the weight force into two components
parallel and perpendicular to ramp.

Result - Down slope force F m g sin ?
- Normal force N m g cos ?
About PowerShow.com