CHAPTER 2 ACCELERATION

CONSTANT vs CHANGING SPEED Constant Speed occurs when an object covers the same distance in equal intervals of time. Changing Speed occurs when an object covers different distance in equal intervals of time.

CONSTANT vs. CHANGING VELOCITY Constant Velocity occurs when an object covers the same displacement in equal intervals of time. Changing Velocity occurs when an object covers different displacement in equal intervals of time.

CONSTANT VELOCITY Time (s) Position (m) Constant Velocity Graph constant velocity

CHANGING VELOCITY Time (s) Position (m) Changing Velocity Graph velocity

ACCELERATION Acceleration will take place if there is a change in direction or speed of a moving object.

ACCELERATION Acceleration is the rate of change of velocity.

Observe the animation of the three cars below. Which car or cars (red, green, and/or blue) are undergoing acceleration?

Velocity (m/s) Time (s) Velocity (m/s)

PRACTICE PROBLEM 1 A car’s velocity changes from 0 m/s to 30 m/s in 10 s. Calculate the car’s acceleration.

A car’s velocity changes from 10 km/h to 30 km/h, 30 min later. Calculate the car’s acceleration. PRACTICE PROBLEM 2

Acceleration is positive Acceleration is negative Acceleration is positive Acceleration is negative Positive or Negative acceleration

In Example A, the object is moving in the positive direction (i.e., has a positive velocity) and is speeding up. When an object is speeding up, the acceleration is in the same direction as the velocity. Thus, this object has a positive acceleration.

In Example B, the object is moving in the negative direction (i.e., has a negative velocity) and is slowing down. When an object is slowing down, the acceleration is in the opposite direction as the velocity. Thus, this object also has a positive acceleration.

1-D Constant Acceleration Equations V f = V i + at D f = V i t + ½ at 2 V f 2 = v i 2 + 2a(D f -D i )

Problem #1 If a car accelerates from rest at a constant 4.2 m/s 2, how long will it take for the car to reach a velocity of 37 m/s?

Problem #1 Solution

Problem #2 An airplane starts from rest and accelerates at a constant 2.50 m/s 2 for 30.0 s before leaving the ground. How far did the airplane move before leaving the ground?

Problem #2 Solution

Problem #3 A parachutist descending at a speed of m/s loses a shoe at an altitude of m. What is the velocity of the shoe just before it hits the ground if it’s acceleration is 9.8 m/s 2 ?

Problem #3 Solution

CHAPTER 2 FREE FALL ACCELERATION

Free Fall with Air Resistance

Free Fall without Air Resistance

Video Clips FallPlot.html Free Fall Displacement: How does mass affect free fall?: l.html Moon hammer/feather drop: ml