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# The Physics of Motion and Energy - 8th Grade

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## William Begoyan

on 9 February 2018

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#### Transcript of The Physics of Motion and Energy - 8th Grade

The Physics of Motion

Page 29 in ISN - Page 338-355 in Textbook
By: Mr. Begoyan
Avid EQ: How do we measure movement?
mOTION
An object is in
motion
if its distance from another object is changing.
A
reference point
is used as a comparison for objects in motion.
Motion is relative and can change depending on what point of reference is chosen.

Example: When you are sitting down in a chair in this classroom, you are still moving, either in reference to the moon, in reference to the sun, in reference to other planets, in reference to the center of our galaxy, or in reference to other galaxies.
Distance
is the total length of the path between 2 points.
Displacement
is the length and direction of a straight line between 2 points.
A
vector
is a quantity that consists of both a magnitude and a direction.
Displacement is a vector, distance is not.
SPeed and Velocity
Distance
vs
Displacement
The
speed
of an object is the distance the object travels per unit of time.
Speed
=
Distance
Time
Speed is rarely constant.
The average speed is calculated by dividing the total distance by the total time it took to cover the distance.
Instantaneous speed
is the rate at which an object is moving at any given time.
Velocity
(
v
) is speed in a given direction.
Velocity is also a vector.
What is a reference point?
How is distance different from displacement?
What is a vector?
How do you calculate speed?
Why does velocity qualify as a vector?
Time
Distance
0
5
10
15
20
25
30
5
10
15
20
The slope (rise/run) of a time vs. distance graph represents speed.
Acceleration
Acceleration
is the rate at which velocity changes with time.
Acceleration
is the change in speed (increase or decrease) or a change in direction.
Increasing speed (positive acceleration)
Decreasing speed (negative acceleration)
Change in direction (no speed change).
Acceleration
is calculated by finding the change in velocity per unit of time.
Acceleration =
Final Velocity
Time
Initial Velocity
-
Time (s)
Speed (m/s)
0
5
10
15
20
5
10
15
20
0
5
5
10
10
15
15
20
20
Time (s)
Distance (m)
Acceleration
can be graphed in 2 ways.
1. The slope of a speed vs time graph.
2. The curve formed by distance vs time graph.
Energy
Work
is done when an object is moved a certain distance.
Energy
is the ability to do work.
An object in motion has
kinetic energy.
Kinetic energy depends on both mass and speed.
mass
speed
Kinetic Energy =
1
2
Mass
x
Speed
2
Potential energy
is stored energy that can do work.
Gravitational potential energy
is based on an object's weight and its height relative to a reference point.
Gravitational
potential energy
=
Weight
x
Height
Elastic potential energy
is contained in objects that have been stretched or compressed.
Chemical potential energy
is stored in chemical bonds that can be broken to generate energy.
An object 's combined kinetic and potential energy is called
mechanical energy
.
Energy is routinely transformed from one type to another.
The most common transformation is to
kinetic energy
from
potential energy
.
The
law of conservation of energy
states that energy can not be created or destroyed, only transformed.
Fuel - 100%
(chemical potential energy)
Kinetic energy - 25%
(motion)
Heat - 75%
(thermal energy)
Define acceleration
What are the 2 ways to graph acceleration?
How are work and energy related?
What are the different types of potential energy?
How are potential, kinetic and mechanical energy related?
What does the law of conservation of energy state?
Homework
On page 28, describe (to a 5th grade audience, so use visuals and colors along with words) the following concepts:
1. Distance vs Displacement.
2. Reference points.
3. Potential vs Kinetic energy.
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