1. Student Learning Objectives
Motion
(Chapter 2)
Student Learning Objectives
Compare and contrast terms used to describe motion
Analyze circular and parabolic motion

2. Physics:The Most Fundamental Physical Science
Physics is concerned with the basic principles that describe how the universe works.
Physics deals with matter, motion, force, and energy.
Intro

3. Physics – Areas of Study
Classical mechanics
Waves and sounds
Thermodynamics
Electromagnetism
Quantum mechanics
Atomic and nuclear physics
Relativity
Intro

4. Motion is everywhere – walking, driving, flying, etc.
This chapter focuses on definition/discussion of: speed, velocity, and acceleration.
There are two basic kinds of motion:
Straight line
Circular
If SuperPowers Were Real: Super Speed
Intro

5. Defining Motion Position – the location of an object
A reference point must be given in order to define the position of an object How fast are you moving right now? - Tucker Hiatt
Motion – an object is undergoing a continuous change in position
Description of Motion – the time rate of change of position
A combination of length and time describes motion
Section 2.1

6. How do speed and velocity compare?
Average speed is the amount of distance covered in some amount of time.
Time can only go forward
Why Does Time Move Forward?
Velocity is speed in some direction.
Up, Down
Left, Right
North, South, East, West
–, +
s = d t

7. Vectors Note that vectors may be both positive and negative.
Section 2.2

8. Instantaneous speed
Section 2.2

9. These Practice Problems are presented in class
Scalars are quantities that indicate size, indicate a numerical value.
Vectors are quantities that indicate the size and direction.
The magnitude of a vector is a scalar; it is the size of the vector.
Example: 65 mph North

10. How is acceleration defined?
Acceleration is the change of velocity in some amount of time.
Deceleration is negative acceleration. (opposite direction of motion)
a = Dv t
∆=delta=change

11. A car that maintains a constant speed in a straight line has zero acceleration.
The distance traveled depends on how long the object has been accelerating.
d = (1/2)at2

12. Practice
These Practice Problems are presented in class

13. What causes vertical acceleration?
Objects are accelerated downward because of gravity.
The gravitational pull from the Earth is the same on all objects, so the downward acceleration is the same on all objects, 9.81 m/s2.
Any difference in the net acceleration is due to air resistance.
MythBusters Feather and Hammer Drop

14. Practice
These Practice Problems are presented in class

15. What is terminal velocity?
An object in free fall is only affected by gravity (no air resistance).
Air resistance provides acceleration upward.
Surface area increases air resistance.
Speed increases air resistance.
Terminal velocity occurs when air resistance balances gravity.
What is terminal velocity?
Terminal Velocity

16. What causes circular motion?
In circular motion, a centripetal force (“center-seeking” force) causes a constant change in motion, a constant change in direction.
Objects move in a straight line, unless an unbalanced force changes the motion.
ac = v2 r
Fc = mac

17. Acceleration in Uniform Circular Motion
Although an object in uniform circular motion has a constant speed, it is constantly changing directions and therefore its velocity is constantly changing directions.
Since there is a change in direction there is a change in acceleration.
What is the direction of this acceleration?
It is at right angles to the velocity, and generally points toward the center of the circle.

18. Centripetal (“center-seeking”) Acceleration
Supplied by friction of the tires of a car
The car remains in a circular path as long as there is enough centripetal acceleration.
Centripetal (“center-seeking”) Acceleration

19. Practice

20. Projectile Motion
An object thrown horizontally combines both straight-line and vertical motion each of which act independently.
Neglecting air resistance, a horizontally projected object travels in a horizontal direction with a constant velocity while falling vertically due to gravity.

21. An object thrown horizontally will fall at the same rate as an object that is dropped.

22. The velocity in the horizontal direction does not affect the velocity and acceleration in the vertical direction.
Shoot the Monkey

23. Why does a projectile have a parabolic trajectory?
The addition of the horizontal velocity and the vertical acceleration due to gravity results in a curved path.

24. Projected at an angle (not horizontal)
Combined Horz/Vert.
Components
Vertical
Component
Horizontal
Component + =

25. A projectile's motion in x does not affect its motion in y
A projectile's motion in x does not affect its motion in y! (and vice versa)
Velocity in x is constant if there is no air resistance. Why?
Velocity in y changes. Why?
Harvard Shoots and Drops

26. A projectile will fall a vertical distance (y) each second after reaching maximum height.
The range (x) of a projectile relative to the horizontal plane depends on the object’s horizontal velocity and time of flight.
y = (1/2)gt2
x = vt
MythBusters Bullet Dropped and Shot
Harvard Shoots the Monkey

27. Under real-world conditions, air resistance causes the paths to be non-symmetric. Air resistance reduces the horizontal velocity.

28. Practice

29. More Practice