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