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Transcript of MOTION!
What is motion?
What do you already know?
Describing Speed: S=d/t
Who is faster Usain Bolt or a Cheetah?
The only difference between Speed
and Velocity is the
new component of
Remember: motion is described as an object's change in position over time.
What do you know about speed?
Describe speed the best you can.
What about Velocity; tell me what you know about velocity.
Finally tell me about Acceleration.
The motion of an object is defined by its change of position over a period of time
the length of the route you travel.
the change in position of the object or the distance between the starting and the ending point.
Bolt holds the world record in the 100 meter dash.
Bolt runs an average speed of 10.43 meters per second
The Cheetah holds the record for the fasts burst of speed for a mammal.
The cheetah's average speed is 16.39 meters per seconds
Any combinations of units for distance and time can be used to describe speed.
Example: Kilometers per hour , centimeters
per day , meters per second, miles per hour
The metric system unit for speed is m/s.
m/s = meters/second
YAAAYYYY FINN and Jake are Back
Finn and Jake are being chased by a brain crazy zombie.
The zombie is able to run at 5m/s
If the zombie is able to run 5m/s, Finn and Jake must run at least 6 m/s.
How long must it take them to run a distance of 450m to escape the zombie?
To solve the problem:
Write the equation we are going to use.
Next input the numbers we know.
Solve the equation: t= 450m/6m/s
There are two types of speed we can measure
The speed of an object at any instant.
The total distance traveled by an object divided by the
total time it took.
In this class we will use average speed:
Ex: We can see instantaneous speed anytime we are traveling in a car by looking at the speedometer. That is the speed we are moving in a vehicle at a given point in time.
. It has only
magnitude. It can be represented by a single number.
It has both magnitude and direction. It can be represented by a number and an angle on a coordinate plane.
Increasing velocity is represented by a green arrow.
Decreasing velocity is represented by a blue arrow.
X) Two escalators next to each other going up and down. Each has a speed
of 2 km/h.
Because their direction is opposite, they have different Velocities.
1) If an object continues in the same direction, but
speeds up or slows
it’s velocity has changed.
2) If an object continues at the same speed, but
velocity has changed.
Ways to Change Velocity:
I can run as fast as possible for as long as I like.
I will never change speeds, but my velocity always changes. Why?
Because I am running around a track and my direction always changes.
A graph of distance vs time (or motion graph) is useful in describing and interpreting motion that is linear.
Distance VS. Displacement
Two examples of how to calculate speed when given the Distance and the time.
TRY TO FIND HOW FAR BOLT COULD RUN IN 60 SECONDS IF HE STAY AT THE SAME SPEED THE ENTIRE TIME.
STEP 1: WRITE THE EQUATION:
STEP TWO: FIND ALL GIVEN VARIABLES:
S=10.43m/s & t=60s
Step 3: What is the unknown:
STEP 4: PUT VARIABLES INTO EQUATION:
STEP 5: SOLVE EQUATION:
A scalar quantity is a quantity that just gives magnitude or how much of something.
ex: temperature, speed, how much something cost. Austin is 32 miles away.
A vector quantity is a something that not only tells us the how much part, but also tells me in what directions:
ex: velocity, Austin is 32 miles NORTH
What is motion?
How would you describe it?
Give an example of motion.
A person walks 5 km/h. The train is moving at 80 km/h with respect to the ground. How fast is the person going with respect to the ground?
Frame of Reference
FRAME OF REFERENCE
Any measurement of position, distance, or speed must be made with respect to a frame of reference.
You have gone a distance of 60 m, but your displacement is less than that! You could find it by using the Pythagorean Theorem. Where the displacement is equal to the hypotenuse.
10 m south
50 m east
Then you go 10 m south
Let’s say you go 50 m east.
distance traveled divided by the time it takes to travel that distance
Here is a video-song to help you remember this formula!
A point used to describe the location of something.
Time is always plotted on the X-axis (bottom of the graph). The further to the right on the axis, the longer the time from the start.
Plotting distance against time can tell you a lot about motion. Let's look at the axis:
Distance is plotted on the Y-axis (side of the graph). The higher up the graph, the further from the start.
On a motion graph...
A straight line indicates constant speed
A horizontal line indicates no motion or zero speed
A positive slope shows positive velocity
A negative slope shows negative velocity
A steeper slope = faster speed
Curved line = linear acceleration or a change in speed
Which runner stopped? How can you tell? For how long was the runner stopped? Explain your answers.
A distance-time graph tells us how far an object has moved with time.
• The steeper the graph, the faster the motion.
• A horizontal line means the object is not changing its position - it is not moving, it is at rest.
• A downward sloping line means the object is returning to the start.
Acceleration : A=v/t
The rate at which the velocity of an object is changing
This is a measure of how the velocity of an object changes with respect to time.
Acceleration =change of velocity
The types of acceleration:
1) speeding up – positive acceleration
2) slowing down – negative acceleration
3) changing direction.
Acceleration = final speed - initial speed
Another way to think about acceleration is:
Practice with Acceleration!
X) Suppose a jet starts at rest at the end of a runway. As it takes off, it reaches a
speed of 80 m/s in 20 s.
(Straight down the runway, its speed and velocity are the same.)
final speed - initial
What we know:
What we don't know:
PUT THEM IN THE EQUATION
Solve the equation
Which of the graphs shows that one of the runners started 10 yards further ahead than the other? Explain.
In which of the graphs above are both of the runners running at the same speed? Explain.
Look at the graph below. It shows how three runners ran a 100-meter race. Which runner won the race? Explain your answer.
Do Now: Describe the motion in this graph.