What is Motion? Chapter 9 Section 1 and 3
Mar 26, 2015
What is Motion?
Chapter 9 Section 1 and 3
Reference point
• a place or object used for comparison to determine if something is in motion.
• Suppose you are standing on a sidewalk and your friend rides past you on her skateboard. – Which one of you is moving relative to the Earth?– Are you moving relative to your friend?
Motion • an object is in motion if it changes position
relative to a reference point. • An object moves when its distance from
another object is changing. • Whether an object is moving or not depends
on your point of view (reference point).
Speed
• The distance an object
travels in one unit of time
is it’s speed. • Speed = Distance
Time
Units of Speed = (m/sec) or (km/hr)• Average speed = total distance
total time
Sample Problem: • At what speed did a plane fly if it traveled
1760 meters in 8 seconds?
Practice Problems:
• A car travels 240 kilometers in 3 hours. What is the speed of the car during that time?
• The speed of a cruise ship is 50 km/hr. How far will the ship travel in 14 hours?
• A cyclist travels 32 km during the first 2 hours of riding, and 13 km during the next hour. What is the average speed of the cyclist?
Velocity
• speed in a given direction.
• Velocity = Distance
Time• Note that the
velocity equation is the same as the speed equation
Graphing motion
• Always use a distance vs. time graph (distance on the vertical or y-axis and time on the horizontal or x-axis).
• Slope – tells you the rate of change (speed).• slope = rise
run
Acceleration
• the rate of change in velocity. Refers to increasing speed, decreasing speed, or changing direction.
• (a)=Final Velocity (fv)-Initial Velocity (iv)Time (t)
• a = fv – iv t• Units for Acceleration: km/hr2, km/hr/s or
m/sec2
Practice Problems:
• A roller coaster is moving at 25m/sec at the bottom of a hill. Three seconds later it reaches the top of the next hill, moving at 10m/sec. What is the deceleration of the roller coaster?
• A car is traveling at 60km/hr. It accelerates to 85km/hr in 5 seconds. What is the acceleration of the car?
Graphing Acceleration
• Velocity vs. Time– Velocity on y-axis– Time on x-axis
• The slope of the line gives you the acceleration of the object.
Final Practice Problems• One jet plane is flying east at 880 km/h, and
another plane is traveling north at 880 km/h. Do they have the same velocities? The same speeds? Explain.
• A swimmer speeds up from 1.1 m/s to 1.3 m/s during the last 20 seconds of the workout. What is the acceleration during this interval?
• Describe three different ways to change your velocity when you’re riding a bicycle.
• An object is said to be accelerating if it ___________.
a) speeds up c) changes direction b) slows down d) all of these