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