Free fall is the motion of an object when gravity is the only force acting on it. In free fall, the object’s acceleration is constant and always directed downwards.

What is Free Fall?

Free fall is what happens when an object moves only because of gravity. We pretend there’s no air pushing on it (no air resistance).

So, in free fall, the only thing making the object change its velocity is gravity.

Key Things About Free Fall

  • Constant Acceleration: Objects in free fall always speed up (or slow down if thrown upwards) at the same steady rate. This means they have constant acceleration.
  • Acceleration Due to Gravity ($g$): This special acceleration is called “acceleration due to gravity.”
    • Near Earth’s surface, its value is about 9.8 m/s².
    • We use the symbol $g$ for this value. So, $a = g = 9.8 \text{ m/s}^2$.
  • Always Downwards: The direction of this acceleration is always downwards, towards the center of the Earth.

Interactive Free Fall Simulator

Observe two objects (a bowling ball and a feather) dropped simultaneously. Toggle air resistance to see its effect on their motion and acceleration.

Free Fall: Ball vs. Feather

Air Resistance: OFF (Vacuum)

Ball Acceleration:

9.8 m/s²

Feather Acceleration:

9.8 m/s²

Free Fall and Kinematics

Because free fall involves constant acceleration, we can use all the kinematic equations we just learned!

You simply replace the acceleration symbol ($a$) with $g$ (or $-g$ if you choose ‘up’ as positive).

For example, the equation for final velocity becomes: \(v_f = v_i + gt\) (If we define ‘down’ as the positive direction)

Starting Free Fall

An object can start free fall in a few ways:

  • Dropped: If an object is simply dropped, its initial velocity ($v_i$) is zero.
  • Thrown Upwards: If an object is thrown straight up, it has an initial upward velocity. Gravity will then slow it down, stop it for a moment at the top, and then make it fall downwards.
  • Thrown Downwards: If an object is thrown straight down, it has an initial downward velocity, and gravity will make it speed up even faster.

Interactive Match: Free Fall

Test your understanding of the key terms associated with free fall.

Click a term and then its matching meaning. Match all pairs to complete!

Why Should I Care?

Understanding free fall helps you:

  • Explain why things fall the way they do.
  • Solve problems about falling objects, like how long it takes for something to hit the ground.
  • It’s a basic step to understanding more complex motions, like throwing a ball (projectile motion).

💡 Quick Concept Check:

If you drop a rock and a feather at the same time (in a vacuum, meaning no air), which one hits the ground first?

Click to Reveal Answer
In a vacuum (no air resistance), both the rock and the feather would hit the ground at the **same time**. This is because gravity causes all objects to accelerate downwards at the same rate ($g$), regardless of their mass.
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