1dkinematics
DESCRIPTION
Basic MechanicsTRANSCRIPT
04/18/23 3
Question
TRUE or FALSE:
The displacement of an object for a round trip between two locations is always greater than zero.
04/18/23 4
Question
TRUE or FALSE:
The displacement of an object during any time interval is always greater than or equal to the distance it travels during the same time interval
04/18/23 5
Example. The diagram below shows the position of a cross-country skier at various times. At each of the indicated times, the skier turns around and reverses the direction of travel. In other words, the skier moves from A to B to C to D.
• Use the diagram to determine the resulting displacement and the distance traveled by the skier during these three minutes.
04/18/23 6
• Now for a final example. A football coach paces back and forth along the sidelines. The diagram below shows several of coach's positions at various times. At each marked position, the coach makes a "U-turn" and moves in the opposite direction. In other words, the coach moves from position A to B to C to D.
04/18/23 7
04/18/23 9
Velocity and Speed
Speed – “how fast the object is moving” velocity – “the rate at which the body changes position”
http://www.physicsclassroom.com/Class/1DKin/U1L1d.html
04/18/23 13
Archimedes ran 100m for 12s towards the positive x-direction. He backtracked 50m walking for 30s. What is his average speed? What is his average velocity?
Example
04/18/23 14
Average and Instantaneous speed
Average speed – just distance over time (average of all inst. speeds)
Instantaneous speed – speed at a particular instant of time
04/18/23 16
Question
An object moves along the x-axis as shown in the figure. At which point is the magnitude of its velocity minimum?
04/18/23 17
Question
Scooby doo cannot understand the difference between average and instantaneous velocity. Help Scooby by explaining to him like you would a 2nd year high school student and give an example of each.
04/18/23 18
Acceleration
The rate of change in velocity
Could be:
1. change in the magnitude 2. change in direction
04/18/23 34
Motion with constant acceleration
Average velocity
0
2avev v
v
0
avex x
vt
True only for motions with constant acceleration
04/18/23 35
Motion with constant acceleration
20 0
12
x x v t a t
0v v a t
2 20 2v v a x
Kinematic equations
04/18/23 36
Example
Toto, a famous drag racer, revved up his car and traveled along a straight horizontal road accelerating from rest at 2 m/s towards the East. What is Toto’s velocity after 5 s? What is his displacement from his initial position x=0m after 5 s?
04/18/23 38
Free-falling bodies
Presence of gravitational force due to Earth causes the ball to accelerate.
04/18/23 40
Free-falling bodies
Negative sign of the gravitational acceleration indicates “downward” direction.
04/18/23 42
Kinematic Equations for free-falling objects
20 0
12
x x v t a t
0v v a t
2 20 2v v a x
Free-fallIn general
20 0
12
y y v t g t
0v v g t
2 20 2v v g y
04/18/23 45
Question
What if these two identical objects were joined together, what happens to their acceleration? Will it double? Will be halved? Will remain the same?
04/18/23 46
Question
If you drop an object in the absence of air resistance, it accelerates downward at 9.8m/s2. If instead you throw it downward, its downward acceleration after release is
a) Less than 9.8m/s2
b) 9.8m/s2
c) more than 9.8m/s2
04/18/23 47
Example
Zoe, the red, falls over a 20.0-m ravine. What is the vertical component of his velocity right before he hits the ground?