1. Chapter 12 Matter in Motion
Section 1
Measuring Motion

2. Observing Motion
A neutron star is the core of a dead star. This one has been observed to be traveling 400,000 mph after its parent star exploded.
Motion is described as a change in position over time when compared to a reference point.
A reference point is a location that appears to stay in place.
Reference point
5.1 billion miles
400,000 miles per hour

3. Speeds of different objects
Snail 0.03 mph or 1.3 cm/sec
Human = 30 mph or 13.3 m/s
Speed of Sound = 760 mph or 337 m/s
Car = 776 mph or 345 m/s
Jet = 2,200 mph or 978 m/s
Rocket = 35,000 mph or 15,555 m/s
Speed of Light = 186,280 miles per sec or 300,000,000 m/s
or 670,608,000 mph

4. Speed depends on distance and time.
The following rate can be used to calculate speed
Include the proper units
m/s, km/h, mph
Distance
Speed
Time

5. Examples
What is your average speed if you walk m in half an hour? d r t

6. You traveled for 6 ½ hours at 110 km/h. How far did you travel?
How long will it take to travel 810 meters at a rate of 15 m/s? d d r t r t
d = 715 km

7. Speed vs Velocity Velocity is speed in a particular direction
Example
m/s
Km/hr
m/s forward
Km/hr south
Velocity changes as speed or direction changes
Examples
A car speeding up or slowing down
A rollercoaster turning
A wheel spinning
All examples of a change in velocity
speed
velocity

8. Combining Velocities Velocities in the same direction can be added:
Example
Car at 10 m/s
Ball at 5 m/s
Combined velocity = 15 m/s
Velocities in opposite directions work against each other
Example
Car at 10 m/s
Ball at 10 m/s
Combined velocity = 0 m/s

9. `
Since we were very young we have learned to add velocities together to make objects move faster and/or farther.

10. Means “change in velocity”
Acceleration
Acceleration is the rate at which velocity changes (DV)
Examples
Speed up
Slow down
Change direction
Use the following formula to calculate acceleration
Units m/s/s (also written m/s2 )
Means “change in velocity”

11. Contiunous Acceleration
Spinning is considered to be accelerating continuously since the direction is constantly changing.

13. Acceleration Examples
An airplane goes from 150 m/s to 50 m/s in 20 seconds. What is the acceleration?
A car goes from a stop to 21 m/s in 6 seconds. What is the acceleration?
A = 3.5 m/s2
A = -5 m/s2
Negative acceleration means the object is slowing down.
Positive acceleration means the object is speeding up.

14. Graphing Speed SLOPE = rise = distance Y-axis
run time
Steeper SLOPE means faster speed
SLOPE represents speed
DISTANCE
Shallow SLOPE means slower speed
X-axis
TIME

15. Graphing Speed SLOPE = rise = distance run time
A downward SLOPE (or negative SLOPE) means the object is coming closer.
DISTANCE
TIME

16. Section 2 Force A force is a “push” or “pull” on an object. Examples
Forces have both size and direction.
Measured in newtons (N)
Examples
Gravity (downward pull due to the size of the objects involved)
Kicking a soccer ball (causes the object to change direction)

17. Forces in Combination (Net Force)
Forces in the same direction add together
Two train engines pulling a large train.
4 jet engines pushing an airplane
How many students does it take to push a school bus?
Forces in opposite directions subtract from each other.
Balanced forces create no motion.
One student trying to push a bus.
Tug-o-war between equally strong people
Unbalanced forces create motion.
Lifting a ball defeats the force of gravity

18. Forces in the same direction are added together to determine net force.
example: moving a car
20 N left
+ 5 N left
25 N Left
20 N
5 N

19. Forces in different directions are subtracted from one another.
Example: a tug of war
(You subtract the smaller force from the larger force)
30 N Right
20 N Left
10 N Right
30 N
20 N

20. Elastic Forces Tension Compression
A magnitude of pulling force on an object
The stretching of an object
Compression
A magnitude pushing force on an object
The squeezing of an object

21. Section 3 Friction
Friction is a force that opposes motion between two surfaces that are touching.
The amount of friction depends on
the force pushing the objects together
the roughness of the surfaces
Friction occurs because all objects have mass and even smooth objects are not perfectly smooth.
“Hills and valleys” are always present.

22. Types of Friction: Kinetic Friction (motion)
Sliding Friction
- one surface grinding over another
- example
box across the floor
Rolling Friction
- one surface rolling across another
- example
wheels, axles, ball-bearings

23. Fluid Friction
- one object moving through a fluid (air, water, oil, etc)
- example
swimming, flying, parachute

24. Friction also exists when objects are not moving.
“Static” means not moving.
Static Friction
- maximum friction experienced before the object begins to slide, roll or move through a fluid
SLIDING
STATIC
Low
High
FRICTION-O-METER

25. In space, no air means no fluid friction.
Flight requires some fluid friction to hold the plane up
Lift
Thrust
Drag
(air friction)
Gravity
Fast fish
Slow fish

26. Ways to Change the amount of friction
Reducing friction
Lubricant
Oil
Smoother surface
Waxed surface, Teflon
Change sliding to rolling
Handcart, wheel-barrow
Reduce the force pushing the objects together (less weight)
Unload, lift
Increasing friction
“Sticky” substances
Glue, tape
Increase the force pushing the objects together
Extra weight, “elbow grease”, brakes on a car
Rougher surface
Sand on the road, cleats