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Explore how gravity causes objects to accelerate when they fall toward Earth.
If you dropped a heavy hammer and a light feather on the Moon, which one would hit the ground first? The answer reveals a hidden law of the universe that governs everything from falling apples to orbiting satellites.
In physics, an object is in free fall when the only force acting upon it is gravity. On Earth, we usually don't see true free fall because of air resistance (or drag), which pushes up against falling objects. However, in a vacuum—a space where all air has been removed—a feather and a bowling ball will fall at the exact same rate! This is because gravity pulls on all masses with the same acceleration, regardless of how heavy or light they are. Without air to slow the feather down, it keeps pace with the heavy ball perfectly.
Quick Check
Why do a leaf and a stone fall at different speeds on a normal windy day?
Answer
Because of air resistance. The air pushes up against the leaf more effectively than the stone, slowing it down.
When an object falls toward Earth, it doesn't just fall at a steady speed; it accelerates. This means it gets faster and faster every single second. Scientists have measured this specific rate of acceleration and call it . On Earth, the value of is approximately ****. This number tells us that for every second an object is in free fall, its downward velocity increases by meters per second. Whether you drop a marble or a refrigerator, gravity tries to add that same to its speed every second.
Imagine a stone is dropped from a high bridge and falls for seconds. How fast is it going right before it hits the water? 1. Identify the time: . 2. Identify gravity: . 3. Apply the formula: . 4. Calculate: .
Quick Check
If a ball has been falling for seconds, what is its current velocity?
Answer
A skydiver jumps from a plane. If we ignore air resistance, how many seconds would it take for the skydiver to reach a speed of ? 1. We know and . 2. We need to find . Rearrange the formula: . 3. Plug in the numbers: . 4. Calculate: .
What would happen if you dropped a hammer and a feather at the same time in a vacuum?
What is the approximate value of acceleration due to gravity on Earth?
If an object falls for seconds in a vacuum, its velocity will be .
Review Tomorrow
Tomorrow morning, try to remember the specific value of 'g' and explain to someone why a heavy ball doesn't fall faster than a light ball in a vacuum.
Practice Activity
Find a safe place to drop two different objects (like a crumpled piece of paper and a flat piece of paper). Observe the difference, then crumple the flat one and try again to see how air resistance changes!