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/s 2 ), downward g = m/s 2 (use this for calculations), the negative means downward The textbook sometimes rounds this to 10 m/s 2 for conceptual reasons

Free Fall – How Far (Table 2.3 on p. 20) Falling Time (s)Falling Distance (m) t½ g · t 2

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) tg · t

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) tg

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 Formulas Type of Problem EquationKey Words Notes Free Fall (distance) d = ½ g · t 2 Drop Dropped Falling d = distance (m) g = 9.81 m/s 2 accel. of gravity t = time (s) Free Fall (velocity) v = g · t Drop Dropped Falling v = velocity (m/s) g = 9.81 m/s 2 accel. of gravity t = time (s)

Homework Read Chapter 2 – Linear Motion (p ) Outline the chapter with bullet points (at least 18 minimum) Answer question 1-25 on page in complete sentences Next test will cover p in the book (in 2 weeks?) Pop Quiz in the near future

Calculations: 1.Calculate the change of displacement for each trial 2.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 and outline with 3 pages of notes. Answer question 1-25 on page in complete sentences Δd sight = 0.19 m; Δd hearing = 0.26 m; Δd touch = 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.