Post on 20-Sep-2019
transcript
MotionRecognizing, Describing, and Measuring Motion
Recognizing Motion
An object is in motion when its distancefrom another object is changing.
Whether an object is moving or not depends on your point of view.
Motion and Reference Points An object is in motion if it changes position
relative to a reference point.
A reference point is a place or object used for comparison to determine if something is in motion.
Measuring Motion
We measure motion with: SPEED
VELOCITY
ACCELERTATION
SPEED
The distance an object travels per unit of time.
SPEED
speed =
s =
km / h
m / s
mi / h (mph)
TIME
time =
t =
h
min
s
DISTANCE
distance = speed x time
d = s t
m
km
mi
Average Speed
Most objects do not move at constant speeds for very long.
Think about how many stops you have to make on your way to school each day.
To calculate average speed, is the total distance divided by the total time.
Solving Problems
Step 1: Write the FORMULA.
Step 2: Fill in the VALUES.
Step 3: SOLVE with UNITS.
No Naked Numbers!
Velocity
Knowing the speed of an object will not tell you everything about its motion.
Velocity is the SPEED & DIRECTION of an object.
Velocity changes if either speed or direction changes.
17 km/h north 25 mph east 0.98 ft/s upward 3.06 m/s left
Acceleration
Acceleration is the rate at which velocity changes.
It refers to increasing speed, decreasing speed (deceleration), or changing direction.
Acceleration
Positive Acceleration = Speeding Up
Negative Acceleration = Slowing Down
(Deceleration)
You can be in motion but have zero acceleration!
Calculating Acceleration
To determine the acceleration of an object, you must calculate the change in velocity during each unit of time.
The formula for this is:
Acceleration = =
Graphing Motion
Graphs can be used to represent motion.
a.k.a. Velocity Graphs or Speed Graphs
This type of graph shows the change in position (a.k.a. distance traveled) over time.
The slope of the line tells you the speed.
speed =
Distance – Time Graphs
Graphing MotionDistance – Time Graphs
No motion.
No velocity.
No acceleration.
Graphing MotionDistance – Time Graphs
No change in motion.
Constant velocity.
No acceleration
Object is in motion
Steeper slope means faster speed!
Graphing MotionDistance – Time Graphs
No change in motion.
Constant velocity.
No acceleration.
Object is in motion.
Steeper slope means faster speed!
Graphing MotionDistance – Time Graphs
What is the difference?
The first one is “going away”.
The second one is “going back home”.
Graphing MotionDistance – Time Graphs
Changing motion.
Increasing velocity.
Positive acceleration.
The object is speeding up!
Graphing MotionDistance – Time Graphs
Changing motion.
Decreasing velocity.
Negative acceleration.
The object is slowing down!
Graphing Motion
a.k.a. Velocity-Time Graphs
or Acceleration Graphs
Look at the DIFFERENT axis labels!
Speed – Time Graphs
Graphing MotionSpeed – Time Graphs
Constant velocity.
No acceleration.
The object is staying at the same speed!
No MotionNo SpeedNo VelocityNo Acceleration
Graphing MotionSpeed – Time Graphs
Increasing velocity.
Positive acceleration.
The object is speeding up!
Graphing MotionSpeed – Time Graphs
Decreasing velocity.
Negative acceleration.
The object is slowing down!
Calculating Acceleration
Lets Try: A car advertisement states that a certain car can
accelerate from rest to 90 km/h in 9 seconds. Find the car’s average acceleration.
An bird accelerates from 15 m/s to 22 m/s in 4 seconds. What is the eagle’s average acceleration?
Negative Acceleration (Deceleration)
Try this problem:
A truck slams on his brakes and slows from 50 mi/hr to 10 mi/hr in 8 seconds. What is his acceleration?
Zero Acceleration
Is it possible to be in motion and have zero acceleration?
YES!
What if you are traveling at 80 km/hr and 10 seconds later, your velocity is still 80 km/hr?
Your acceleration is ZERO! You have constant speed.
Constant Acceleration
Think of a situation where you would be accelerating at a constant rate?
Hint: Remember that a change of direction is also acceleration.
Circular motion is constant acceleration because the direction is constantly changing.