Introduction to One-Dimensional Motion

Quantities associated with motionScalar Quantities do not have direction.

Scalar quantities only have magnitude (how much)• Ex: 15 meters, 28 km/s

Vector Quantities have both magnitude and direction.• Ex: 15 meters to the right, 28 km/s to

the North

What’s the difference between distance and displacement?

• Distance: the total magnitude traveled• For example, if you have to take the long way

around a traffic jam, your distance increases• Displacement: the shortest distance from the

starting point to the ending point• Draw & label this picture on your notes

What is average speed?

What is Average Velocity?

Units For Speed and Velocity

In science, we use the metric system and distance & displacement are measured in meters (m)Time is measured in seconds (s) no matter what measurement system you are usingTherefore, speed and velocity are both measured in the same units (m/s)

Speed & Velocity Examples

•Speed is distance divided by time• 2 cm/s

•Velocity is displacement divided by time and includes and has direction• 2 cm/s west

West

More Velocity Examples

• If the runner goes around a 400m circular track 2 times, what is his displacement?• Straight line distance from beginning

to end = zero •What is the distance covered?•2 times the circumference of the

circle = 800m

Try these Speed/Velocity Problems #1 and #2

1. A car travels 1000 m in 50s. What is the car’s speed?•Speed = distance/time

= 1000 m/50 s = 20 m/s2. A car travels 1000 m north in 50s. What is the car’s velocity?•Velocity = displacement/time

= 1000 m/50 s = 20 m/s, north

Sample Problem #3• A car travels 500 m east, 1000 m west and

then 2000 m east again. It does this in a time of 100 seconds. What is the car’s average speed?

Speed = distance/time = 3500 m/100 s = 35 m/s

•What is the car’s average velocity? Velocity = displacement/time

= 1500 m east/100 seconds = 15 m/s, east

What is the difference between average velocity and instantaneous velocity?

• Average Velocity: • Total Displacement divided by total time

• Instantaneous Velocity: Velocity at a certain moment in time

• Ex: A school bus takes 45 seconds to travel 25 meters. What is the average velocity?

• What is the instantaneous velocity when it stops?

Using Graphs to Calculate Speed

Practice Problems

1. A dog runs 15.3 m/s for 32 seconds. How far does he go?

2. How long does it take to go 12 m in a car travelling 28 m/s?

3. What is the speed of an airplane that flies 2000 km for 2.5 hours?

Practice Problems