1. Galileo and Speed

2. Objectives
1. Explain the Galileo’s concept of inertia
2. Distinguish between speed and
velocity
3. Perform calculations involving speed,
time, and distance
4. Create and interpret distance-time
graphs

3. Aristotle
 Natural motion – at rest
 Unatural motion– force
required by human or
animal
 Force = push or pull

4. Galileo
 Except for friction
– objects fall at
the same time
 Force required to
start an object,
but not to keep it
moving

6.  Hypothesized – if friction was absent the ball
would move forever
 Inertia – property of objects motion

7.  Galileo – first to measure speed
 Speed = distance/time

8.  Average speed
 Instantaneous speed – speed at any given moment
 Constant speed – doesn’t slow down or speed up

9. Velocity
 Both speed and direction
 Car travels 60 km/hr north
 Constant velocity – doesn’t slow down,
speed up, or change direction
 Motion that’s not constant - acceleration

10.  What is the average speed of a cheetah that
sprints 100m in 4s? How about 50m in 2s?
 The speedometer on a bicycle moving east
reads 50 km/h. It passes another bicycle
moving west at 50 km/h. Do both bikes have
the same speed? Do they have the same
velocity?

11. Problem
 Are the cars in front of the school
speeding?