1. Warm up day 19
a=Vf-Vi T
A car is at a stoplight. The light turns green and the car acclerates from rest to 40m/s in 13 seconds. What is the acceleration rate?

2. Acceleration the rate at which velocity changes
occurs when something is speeding up (+), slowing down (-), or changing direction
Formula:
typically expressed in units of m/s2
is always changing when traveling in a circle - centripetal
a = vf – vi t
Describe the car’s acceleration
Describe the car’s acceleration
a = 0 m/s – 10 m/s = -5 m/s2
2 s
a = 50 m/s – 0 m/s = 10 m/s2
5 s

3. Understanding Acceleration
Time
(sec)
Velocity
(m/s) 1 2 3 4 5
When dropped, the ball will accelerate toward the center of the Earth at a rate of m/s2 because of gravity. What will be the ball’s velocity at each second?
9.8
19.6
29.4
39.2
49.0

4. Practice Problems - Acceleration
Tina starts riding her bike down a hill with a velocity of 2 m/s. After six seconds, her velocity is 14 m/s. What is Tina’s acceleration?
2. A motorcyclist goes from 35 m/s to 20 m/s in five seconds. What was his acceleration?
a = vf – vi t
14 m/s -
2m/s
2 m s2
a = =
6 s
a = vf – vi t
a =
20 m/s -
35 m/s
-3 m s2 =
5 s

5. Describe the student’s acceleration as she travels to class?
Velocity-Time Graph
Shows how acceleration relates to velocity and time 50 40 30 20 10 60 70 80 90
100
Time (seconds) 2 4 6 8 12
Velocity (meters/second)
This velocity-time graph will show a student’s acceleration as she returns to class after lunch.
Describe the student’s acceleration as she travels to class?

6. Describe What’s Happening (velocity-time graphs)
Constant, positive velocity; away from starting point
Constant, zero velocity
Constant, negative velocity toward the starting point
What do all of these velocity – time graphs have in common?
How do these relate to the distance – time graphs? D T D T D T

7. Applying What You Have Learned
Describe what’s happening in the graphs. How would it look on a distance-time graph? T D T D T

8. Assignment:
Complete the acceleration practice problems from yesterday.
In your notebook draw a velocity time graph for the following trip.
A student accelerates from rest to 3m/s in 4 seconds. The student travels at this speed fro 4 seconds then stops. The student sits still for 3 seconds then acceleratets back up to 3m/s in 2 seconds.

9. Momentum p = mv Formula: a measure of mass in motion is a vector
the product of an object’s mass and velocity
Formula:
typically expressed in units of kg·m/s
is in the same direction as the velocity
makes an object harder to stop or change direction as it increases
can be transferred
is conserved
p = mv
20 kg
Which object has more momentum – the curling rock or the hockey puck? Explain your reasoning.
Describe the scenario where the puck would have more momentum than the curling rock?
0.17 kg

10. Practice Problems - Momentum
What is the momentum of a 7.3 kg bowling ball moving at 8.9 m/s?
2. At a velocity of 8.5 m/s, Tim moves down a hill on an inner tube. If his mass is 59 kg, how much momentum does he have?
p = mv
p =
(7.3 kg)
(8.9 m/s) =
65 kg·m/s
p =
(59 kg)
(8.5 m/s)
p = mv =
502 kg·m/s

11. Frame of Reference (Reference Point)
a stationary location or object to which you compare other locations or objects
none are truly stationary relative to all others – what is not moving in one is moving in another
Task
Using your body as the frame of reference, describe your classmate’s motion as s/he walks to the classroom door. How does your frame of reference impact your description compared to that of others?
How does frame of reference explain why people thought the Earth was in the center of all celestial bodies?

12. Vector a quantity that has both direction and magnitude (size)
drawn as an arrow which shows direction and magnitude (length of arrow)
consists of two parts: tail and head
Head
Tail
Consider the vectors above. Describe the direction and relative magnitude (speed) of each car based on the vector.

13. Combining Vectors can be combined/added
What is the total velocity for each of the people/animals on the conveyor belt?
3 m/s
2 m/s
1 m/s
2 m/s
3 m/s
dog
belt
2 m/s
belt
ram
3 m/s
man’s total
velocity
2 m/s
belt
1 m/s
man
1 m/s
dog’s total
velocity
ram’s total
velocity = 0 m/s
2 m/s
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