Object Thrown Upward

1
Object Thrown Upward
2
Explaining Motion
3
Aristotle again
Natural and Violent Motion
Aristotle asserted that natural motion proceeds
from the nature of an object, dependent on what
combination of the four elements earth, water,
air and fire.
4
The essential thing about violent motion was that
it was externally caused and was imparted to
objects they moved not by their nature but
because of pushes and pulls.
5
Galileo was the first to suggest that
constant-speed, straight-line motion was just as
natural as at-rest motion. This property of
remaining at rest or continuing to move in a
straight line at a constant speed is known as
inertia.
6
Galileos inclined planes revisited
Slope upward speed decreases
Slope downward speed increases
No slope. Does speed change?
7
Initial
Final position
Where is the final position?
8
What is the main difference between the everyday
usage of the word inertia and its use in Physics?
9
Newtons first law of motion
The first law incorporates Galileos idea of
inertia and introduces a new concept, force.
10
The stretch of the spring is a measure of the
applied force.
11
Every object continues in its state of rest, or
of uniform motion in a straight line, unless it
is compelled to change the state by forces
impressed upon it.
12
Examples

1. The room you are sitting in is currently moving
   at about 400 m/s as a result of Earth spinning
   about its axis. The walls of the room are
   attached to Earth but, if you jump up into the
   air, you are not. Why does the west wall not move
   across and strike you?
2. Assume that you are pushing car across a level
   parking lot. When you are stop pushing, the car
   comes to stop. Does this violate Newtons first
   law? Why?
3. Why does a tassel hanging from the rearview
   mirror appear to swing forward as you apply the
   brakes?

13
If you were traveling toward a distant star and
you ran out of fuel, would your spaceship slow
down and stop? Explain.  
14
Vectors and Scalars
15
Addition of Vectors Graphical Methods
16
(No Transcript)
17
If the vectors are not along the same line?
18
(No Transcript)
19
Tail-to-tip method of adding vectors

1. On a diagram, draw one of the vectors call it
   V1 to scale.
2. Next draw the second vector V2, to scale,
   placing its tail at the tip of the first vector
   and being sure its direction is correct.
3. The arrow drawn from the tail of the first vector
   to the tip of the second represents the sum, or
   resultant, of two vectors.

20
Tail-to-tip method can be extended to three or
more vectors
21
Examples

1. In everyday use, inertia means that something is
   hard to get moving. Is this the only meaning it
   has in physics? If not, what other meaning does
   it have?
2. How would you determine that two objects have the
   same inertia?
3. When a number of different forces act on an
   object, is the net force necessarily in the same
   direction as one of the individual forces? Why?
4. Modern cars are required to have headrests to
   protect your neck during collisions. For what
   type of collision are these headrests most
   effective?

22
Newtons Second Law
The net force on an object is equal to its mass
times its acceleration and points in the
direction of acceleration Fnet ma
23
Units of Force
1 newton (N) 1 Kg m/s2
24
Examples

1. Forces of 4 N and 6 N act on the object. What is
   the minimum value for the sum of these two
   forces?
2. Two ropes are being used to pull a car out of a
   ditch. Each rope exerts a force of 700 N on the
   car. Is it possible for the sum of these two
   forces to have a magnitude of 1000N? Explain your
   reasoning.
3. If the net force on a boat is directed due east,
   what is the direction of the acceleration of the
   boat? Would your answer change if the boat had a
   velocity due north but the net force still acted
   to the east?

25
Examples

1. Describe the force(s) that allow you to walk
   across the room.
2. You are analyzing a problem in which two forces
   act on an object. A 200 N force pulls to the
   right, and a 40 N force pulls to the left. Your
   classmate asserts that the net force is 200 N
   because that is the dominant force that is
   acting. What is wrong with that assertion?