Acceleration of Gravity and Free Fall

9/12/13

Bellwork What is the difference between velocity

and acceleration? Velocity is the rate at which an object

change its distance Acceleration is the rate at which an

object change its velocity

Recap

Velocity is speed with direction Speed is velocity without direction Both use the variable “v” in equations Most common unit of measurement in

this class meters per second (m/s)

Recap

Acceleration is the rate an object is changes its velocity.

(m/s)———

(s)

Instantaneous and Average Velocity (recap) Instantaneous velocity is how fast you

are going at that moment (speedometer at that moment)

Average velocity is your speed over a period of time (overall distance and total time)

Free Fall

Free Fall: The motion of an object under the influence of the gravitational force only (no air resistance)

(i.e.) An object that is dropped or falling (e.g.) Dropping a tennis ball or meter

stick

Acceleration of Gravity At the surface of the Earth it equals:

9.81 m/s/s (m/s2), downward g = -9.81 m/s2 (use this for calculations),

the negative means downward The textbook sometimes rounds this to

10 m/s2 for conceptual reasons

Free Fall – How Far (Table 2.3 on p. 20)

Falling Time (s) Falling Distance (m)

0 0

1 5

2 20

3 45

4 80

5 125

t ½ g · t2

Free Fall – How Far

Free Fall – How Far

Free Fall – How Far

An object in free fall, will fall a greater distance each second it falls

(Falls greater distances)

Free Fall – How Fast (Table 2.2 on p. 17)

Falling Time (s) Falling Speed (m/s)

0 0

1 10

2 20

3 30

4 40

5 50

t g · t

Free Fall – How Fast

Free Fall – How Fast

An object in free fall, will increase is velocity by 9.81 m/s, downward, every second it falls

Free Fall – Acceleration (on p. 17)

Falling Time (s) Falling Accel. (m/s/s)

0 10

1 10

2 10

3 10

4 10

5 10

t g

Free Fall – Acceleration

• Acceleration is constant at 9.81 m/s/s, downward

Free Fall – Acceleration

Objects fall at a constant acceleration of 9.81 m/s/s, downward

New FormulasType of Problem

Equation Key Words

Notes

Free Fall (distance)

d = ½ g · t2 Drop

Dropped

Falling

d = distance (m)

g = 9.81 m/s2

accel. of gravity

t = time (s)

Free Fall (velocity)

v = g · t Drop

Dropped

Falling

v = velocity (m/s)

g = 9.81 m/s2

accel. of gravity

t = time (s)

Homework Read Chapter 2 – Linear Motion (p. 10-24) Outline the chapter with bullet points

(at least 18 minimum) Answer question 1-25 on page 25-26 in

complete sentences Next test will cover p. 10-32 in the book (in

2 weeks?) Pop Quiz in the near future

Calculations:1. Calculate the change of displacement for each trial2. Calculate the average displacement for each sense.3. Using a T-Chart (3 total), calculate each reaction time

by using the average displacement (in meters).4. Using a T-Chart (3 total), calculate the average

velocity that the meter stick is traveling as you catch it for each of the senses.

Questions: (Answer in complete sentences.)1. What sense had the fast reaction time?2. Was your pre-lab prediction right?3. Why do you think this was quicker than your other

senses?4. How does your best reaction time compare to hitting

a base ball thrown by a major league pitcher? (t = 0.18s)

5. What factors might have contributed to your reaction time being too slow or quick? Be specific!

Reaction Time Alternative Assignment

• Read pages 10-24 and outline with 3 pages of notes.

• Answer question 1-25 on page 25-26 in complete sentences

• Δdsight = 0.19 m; Δdhearing = 0.26 m; Δdtouch = 0.21 m

1. Using a T-Chart (3 total), calculate each reaction time by using the average displacement.

2. Using a T-Chart (3 total), calculate the average velocity that the meter stick is traveling as it is caught for each of the senses.