Ch 8 Motion 4.ppt well as astronomical objects, such as spacecraft, planets, stars.

In physics, motion is when an object changes its position with respect to a reference point in a given time. Motion is mathematically described in terms of displacement, distance, velocity, acceleration, speed, and frame of reference to an observer, measuring the change in position of the body relative to that frame with a change in time. The branch of physics describing the motion of objects without reference to their cause is called kinematics, while the branch studying forces and their effect on motion is called dynamics.

If an object is not in motion relative to a given frame of reference, it is said to be at rest, motionless, immobile, stationary, or to have a constant or time-invariant position with reference to its surroundings. Modern physics holds that, as there is no absolute frame of reference, Isaac Newton's concept of absolute motion cannot be determined.[1] Everything in the universe can be considered to be in motion.[2]: 20–21 

Motion applies to various physical systems: objects, bodies, matter particles, matter fields, radiation, radiation fields, radiation particles, curvature, and space-time. One can also speak of the motion of images, shapes, and boundaries. In general, the term motion signifies a continuous change in the position or configuration of a physical system in space. For example, one can talk about the motion of a wave or the motion of a quantum particle, where the configuration consists of the probabilities of the wave or particle occupying specific positions. In physics, the motion of massive bodies is described through two related sets of laws of mechanics. Classical mechanics for super atomic (larger than an atom) objects (such as cars, projectiles, planets, cells, and humans) and quantum mechanics for atomic and sub-atomic objects (such as helium, protons, and electrons). Historically, Newton and Euler formulated three laws of classical mechanics:

First law: In an inertial reference frame, an object either remains at rest or continues to move in a straight line at a constant velocity, unless acted upon by a net force.
Second law: In an inertial reference frame, the vector sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration a of the object:
F
→
=
m
a
→
{\displaystyle {\vec {F}}=m{\vec {a}}}.
If the resultant force
F
→
{\displaystyle {\vec {F}}} acting on a body or an object is not equal to zero, the body will have an acceleration
a
{\displaystyle a} that is in the same direction as the resultant force.

Third law: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction onto the first body.
Classical mechanics
Main article: Kinematics
Classical mechanics is used for describing the motion of macroscopic objects moving at speeds significantly slower than the speed of light, from projectiles to parts of machinery as well as astronomical objects, such as spacecraft, planets, stars.

1. Ch. 3 & 4Ch. 3 & 4
Motion & ForcesMotion & Forces
II. Describing Motion
 Motion
 Speed & Velocity
 Acceleration

2. Newton’s First LawNewton’s First Law
Newton’s First Law of Motion
An object at rest will remain at
rest and an object in motion
will continue moving at a
constant velocity unless acted
upon by a net force.
motion
constant velocity
net force

3. A. MotionA. Motion
Problem:
Is your desk moving?
We need a reference point...
nonmoving point from which
motion is measured

4. A. MotionA. Motion
Motion
Change in position in relation to
a reference point.
Reference point
Motion

5. A. MotionA. Motion
Problem:
You are a passenger in a car
stopped at a stop sign. Out of the
corner of your eye, you notice a
tree on the side of the road begin
to move forward.
You have mistakenly set yourself
as the reference point.

6. B. Speed & VelocityB. Speed & Velocity
Speed
rate of motion
distance traveled per unit time
time
distance
speed
v
d
t

7. B. Speed & VelocityB. Speed & Velocity
Instantaneous Speed
speed at a given instant
Average Speed
time total
distance total
speed avg. 

8. B. Speed & VelocityB. Speed & Velocity
Problem:
A storm is 10 km away and is
moving at a speed of 60 km/h.
Should you be worried?
It depends
on the
storm’s
direction!

9. B. Speed & VelocityB. Speed & Velocity
Velocity
speed in a given direction
can change even when the
speed is constant!

10. C. AccelerationC. Acceleration
Acceleration
the rate of change of velocity
change in speed or direction
t
vv
a
if

a: acceleration
v
f: final velocity
v
i
: initial velocity
t: time
a
v
f - v
i
t

11. C. AccelerationC. Acceleration
Positive acceleration
“speeding up”
Negative acceleration
“slowing down”

12. D. CalculationsD. Calculations
Your neighbor skates at a speed of 4 m/s.
You can skate 100 m in 20 s. Who skates
faster?
GIVEN:
d = 100 m
t = 20 s
v = ?
WORK:
v = d ÷ t
v = (100 m) ÷ (20 s)
v = 5 m/s
You skate faster!v
d
t

13. D. CalculationsD. Calculations
A roller coaster starts down a hill at 10 m/s.
Three seconds later, its speed is 32 m/s.
What is the roller coaster’s acceleration?
GIVEN:
v
i
= 10 m/s
t = 3 s
v
f
= 32 m/s
a = ?
WORK:
a = (v
f
- v
i
) ÷ t
a = (32m/s - 10m/s) ÷ (3s)
a = 22 m/s ÷ 3 s
a = 7.3 m/s
2a
v
f - v
i
t

14. D. CalculationsD. Calculations
Sound travels 330 m/s. If a lightning bolt
strikes the ground 1 km away from you,
how long will it take for you to hear it?
GIVEN:
v = 330 m/s
d = 1km = 1000m
t = ?
WORK:
t = d ÷ v
t = (1000 m) ÷ (330 m/s)
t = 3.03 s
v
d
t

15. D. CalculationsD. Calculations
How long will it take a car traveling 30 m/s
to come to a stop if its acceleration is
-3 m/s
2
?
GIVEN:
t = ?
v
i = 30 m/s
v
f
= 0 m/s
a = -3 m/s
2
WORK:
t = (v
f
- v
i
) ÷ a
t = (0m/s-30m/s)÷(-3m/s
2
)
t = -30 m/s ÷ -3m/s
2
t = 10 sa
v
f - v
i
t

16. E. Graphing MotionE. Graphing Motion
slope =
steeper slope =
straight line =
flat line =
Distance-Time Graph
A
B
faster speed
constant speed
no motion
speed

17. E. Graphing MotionE. Graphing Motion
Who started out faster?
A (steeper slope)
Who had a constant speed?
A
Describe B from 10-20 min.
B stopped moving
Find their average speeds.
A = (2400m) ÷ (30min)
A = 80 m/min
B = (1200m) ÷ (30min)
B = 40 m/min
Distance-Time Graph
A
B

18. 0
100
200
300
400
0 5 10 15 20
Time (s)
D
i
s
t
a
n
c
e

(
m
)
Distance-Time Graph
E. Graphing MotionE. Graphing Motion
Acceleration is
indicated by a
curve on a
Distance-Time
graph.
Changing slope =
changing velocity

19. E. Graphing MotionE. Graphing Motion
0
1
2
3
0 2 4 6 8 10
Time (s)
S
p
e
e
d

(
m
/
s
)
Speed-Time Graph
slope =
straight line =
flat line =
acceleration
+ve = speeds up
-ve = slows down
constant accel.
no
accel. (constant
velocity)

20. E. Graphing MotionE. Graphing Motion
0
1
2
3
0 2 4 6 8 10
Time (s)
S
p
e
e
d

(
m
/
s
)
Speed-Time Graph
Specify the time period when
the object was...
slowing down
5 to 10 seconds
speeding up
0 to 3 seconds
moving at a constant
speed
3 to 5 seconds
not moving
0 & 10 seconds