Free Fall and Gravity

Definition and Key Concepts

Free fall refers to the motion of objects under the influence of gravity alone, with no other forces acting (such as air resistance or tension). This concept is fundamental in introductory physics, especially when analyzing vertical motion.

• Free fall: Occurs when gravity is the only force acting on an object.

• Gravity (g): The acceleration due to gravity on Earth is always downward.

• Objects in free fall experience constant vertical acceleration.

• Free fall applies whether the object is moving upwards or downwards.

Example: A ball dropped from a building is in free fall until it hits the ground.

Uniformly Accelerated Motion (UAM) Equations

Horizontal and Vertical Motion

When analyzing free fall and other uniformly accelerated motion, we use the UAM equations. These equations relate displacement, velocity, acceleration, and time.

Note: For free fall, (downward).

Solving Free Fall Problems

Step-by-Step Approach

To solve problems involving free fall and UAM, follow these steps:

1. Draw a diagram and list the five variables: initial velocity (), final velocity (), displacement (), acceleration (), and time ().

2. Identify known and target variables.

3. Pick the appropriate UAM equation that does not include the ignored variable.

4. Solve for the unknown.

Example: A ball is dropped from rest from a 100 m tall building. Calculate the ball's velocity right before hitting the ground.

Sample Problems and Applications

Problem 1: Rock Thrown from a Building

A rock is thrown downward from the top of a building and lands in the street below. (a) What is the speed of the rock just before it hits the street? (b) How much time elapses from when the rock is thrown until it hits the street?

• Use the vertical UAM equations to solve for final velocity and time.

• Assume .

Problem 2: Keys Thrown Between Students

One student throws keys to another student below. The second student catches the keys 1.50 s later. (a) With what initial velocity were the keys thrown? (b) What was the velocity of the keys just before they were caught?

• Apply the vertical UAM equations to find initial velocity and final velocity.

• Given time and displacement, solve for unknowns.

Summary Table: Vertical UAM Equations

Additional info: The notes emphasize the importance of identifying knowns and unknowns, and choosing the correct equation based on the variables involved. The examples provided are typical of introductory physics problems involving free fall and vertical motion.