1. Ch 2 notes

2. Motion & Position How do you know the mail truck has moved?
motion – a change in an object’s position due to a reference point
after reference point is chose, a frame reference can be chosen
Figure 1 – pg. 44

3. Motion & Position
frame of reference – a coordinate system in which position of object is measured
x-axis & y-axis are drawn perpendicular to each other & intersect with the reference point
insert Fig. 2 – pg. 45

4. Relative motion
-when you didn’t see an object move, but you know it moved because it’s in a new position/place.

5. Motion & Position
in order to describe motion of an object, need to know distance -how far it has moved –
SI Unit of length or distance is meters (m) or kilometers (km) for longer distances (1 km = 1,000 m)
shorter distances are measured in centimeters (cm) or millimeters (1 m = 100 cm = 1,000 mm)

6. Motion & Position
an object starts at one point and ends up back at the same point you can find the distance and direction it has traveled
displacement – the distance of an object's change in position from the starting point
if an object goes in a single direction, the displacement and distance traveled would be the same

7. Motion & Position
Example: What is the distance the runner ran? What is the runner’s displacement?
Figure 3 – pg. 45

8. Motion & Position when adding displacements check directions
if directions are the same, add displacements
if directions are opposites, subtract displacements
the total displacement will be in the direction of the larger displacement
if directions are not the same or opposite, use math
insert Fig. 4 – pg. 46

9. Speed can also describe how fast an object is moving
need to know how far it travels in a given amount of time
speed – the distance an object travels per unit time
SI Unit for speed is meters per second (m/s)
speed is a rate (any change over time)
rate of growth is how much height changes over time
figure out your heart rate (number of beats per second)

10. Speed speed is the rate of change in position
can calculate speed by dividing distance by time
insert Table 2 – pg. 47

11. Speed
Example: A car traveling at a constant speed covers a distance of 750 m in 25 s. What is the car’s speed?
known: distance (d) = 750 m, time (t) = 25 s
set up problem:

12. Example: A car traveling at a constant speed covers a distance of 750 m in 25 s. What is the car’s speed?

13. Speed
if an object does not speed up or slow down the object is traveling at constant speed
speed calculated by dividing any distance interval over the time it took to travel that distance
usually speed is not constant

14. Speed
when speed changes you can calculate average speed – the total distance traveled divided by the total time of travel
from Fig. 5 the average speed is 5 km divided 0.25 hr
insert Fig. 5 – pg. 48

15. Speed instantaneous speed – the speed at a given point in time
can change instantaneous speed by speeding up or slowing down (speed is different at every point in time)
if an object is moving with constant speed the instantaneous speed does not change (speed is the same at every point in time)

16. Graphing Motion
can graph distance versus time to display the motion of an object over a period of time
dependent variable (y-axis) is distance
independent (x-axis) is time

17. Graphing Motion
Fig. 7 shows the distance traveled by 3 swimmers for 30– minutes
insert Fig. 8 – pg. 50

18. Graphing Motion
Fig. 7 shows the distance traveled by 3 swimmers for 30– minutes
red line: motion of Mary (constant speed of 80 m/min)

19. Graphing Motion
Fig. 7 shows the distance traveled by 3 swimmers for 30– minutes
red line: motion of Mary (constant speed of 80 m/min)
blue line: motion of Kathy (constant speed of 60 m/min)
insert Fig. 8 – pg. 50

20. Graphing Motion
Fig. 7 shows the distance traveled by 3 swimmers for 30– minutes
red line: motion of Mary (constant speed of 80 m/min)
blue line: motion of Kathy (constant speed of 60 m/min)
green line: motion of Julie (no constant speed)
insert Fig. 8 – pg. 50

21. Graphing Motion A straight line at an angle represents constant speed
The steeper the slope, the faster the speed
●A flat line across represents an object at rest (no motion)

22. Velocity speed describes how fast something is moving
velocity describes the speed and direction of a moving object
same unit as speed (m/s)
Example: escalators – people moving at same speed, but since they are moving in opposite directions, their velocities are different

23. Velocity velocity of an object can change, even if speed does not
-changing direction will change velocity
the race cars have a constant speed
but since the cars are changing direction their velocities are changing
insert Fig. 9 – pg. 51

24. Motion of Earth’s Crust
sometimes things move so slowly that you can not feel its motion
the Earth is moving around the sun, while rotating
the continents have moved over time (250 million years)
some plates are moving about 17 cm per year
insert Fig. 11 – pg. 52

25. Momentum
moving objects have a property called momentum that relates how much force is needed to change an objects motion
momentum – property that a moving object has because it has mass & velocity

26. Momentum
would it be easier to stop a slow-moving bike or a fast- moving one?
would it be easier to stop a slow-moving bike or a car going the same speed?
increasing the speed or mass, makes an object harder to stop
insert Fig. 14 – pg. 55

27. Momentum momentum has the symbol “ρ” & its equation is:
SI Unit for momentum is kgm/s
momentum has a direction since it has a velocity
insert Table 3 – pg. 54

28. Momentum known: mass (m) = 80.0 kg, velocity (ν) = 10.0 m/s east
Example: At the end of a race, a sprinter with a mass of 80.0 kg has a velocity of 10.0 m/s east. What is the sprinter’s momentum?
known: mass (m) = 80.0 kg, velocity (ν) = 10.0 m/s east
set up problem:

29. Acceleration
when a car is moving, it goes faster if the gas pedal is pushed down – velocity is changing
acceleration – the rate of change of velocity, which occurs if an object speeds up, slows down, or changes direction

30. Acceleration acceleration has a direction, just as velocity does
if an object is accelerating in the same direction as the velocity (the speed is increasing), the acceleration is positive
if the acceleration is in the opposite direction from the velocity, (an object's speed is decreasing, ) the acceleration is negative
insert Fig. 15 – pg. 56

31. Acceleration
when looking at graphs of speed versus time, you can find out information about acceleration
shape of the curve shows when an object is speeding up or slowing down
insert Fig. 16 – pg. 57

32. Acceleration negative acceleration zero acceleration
positive acceleration

33. Acceleration acceleration is the rate of change in velocity
to calculate acceleration, divide the change in velocity or speed by the length of time interval over which the change occurred
SI Units for acceleration are m/s2
can have a positive or negative value

34. Acceleration
to calculate the change in velocity, subtract the initial velocity from the final velocity
Change in Velocity = Final Velocity – Initial Velocity
= νf – νi

35. if an object is speeding up, it will have a positive acceleration (plane taking off)
takes a plane 20 secs to take off
takes off at a speed of 80 m/s
Acceleration

36. Acceleration
if an object is slowing down, it will have a negative acceleration (skateboarder stopping)
initial speed was 3 m/s
takes 2 seconds to stop

38. A girl was riding her skateboard at 3m/s
A girl was riding her skateboard at 3m/s. It took her 2s to come to a complete stop.

39. Circular Motion
Fig. 17 – horses on a carousel moving in a circular path
speed remains constant – but accelerating since direction of motion is changing
change in velocity is toward the center of the carousel
centripetal acceleration – acceleration toward the center of a curved or circular path (Earth as it orbits the Sun)
insert Fig. 17 – pg. 59

40. Projectile Motion
when you throw something it will not travel in a straight line, it curves downward
anything shot through the air is called a projectile
Earth’s gravity causes projectiles to follow a curved path
projectiles have horizontal & vertical motions (causes curved path)
insert Fig. 18 – pg. 59