What is Free Fall?

S6-SA3-0037

Grade Level:

Class 10

AI/ML, Physics, Biotechnology, Space Technology, Chemistry, Engineering, Medicine

Definition

What is it?

Free fall is when an object moves only under the influence of gravity. This means no other forces like air resistance are significantly acting on it. In free fall, all objects, regardless of their mass, accelerate downwards at the same rate.

Simple Example

Quick Example

Imagine dropping a small stone and a heavy cricket ball from the same height at the same time. If there's no air to slow them down (like in a vacuum), they would both hit the ground at exactly the same moment. This is because both are experiencing free fall.

Worked Example

Step-by-Step

PROBLEM: A stone is dropped from the top of a 45-meter tall building. How long will it take to hit the ground if we ignore air resistance? (Assume acceleration due to gravity, g = 10 m/s^2).

STEP 1: Identify the known values. Initial velocity (u) = 0 m/s (since it's dropped). Displacement (s) = 45 m. Acceleration (a) = g = 10 m/s^2.
---STEP 2: Identify the unknown value. We need to find the time (t).
---STEP 3: Choose the correct kinematic equation. Since we have s, u, a, and want t, the equation s = ut + (1/2)at^2 is suitable.
---STEP 4: Substitute the known values into the equation: 45 = (0 * t) + (1/2) * 10 * t^2.
---STEP 5: Simplify the equation: 45 = 0 + 5t^2, which becomes 45 = 5t^2.
---STEP 6: Solve for t^2: t^2 = 45 / 5 = 9.
---STEP 7: Solve for t: t = sqrt(9) = 3 seconds (time cannot be negative).

ANSWER: The stone will take 3 seconds to hit the ground.

Why It Matters

Understanding free fall is crucial for engineers designing rockets and satellites for ISRO, and for physicists studying planetary motion. It helps space technology experts calculate trajectories and understand how objects behave in space, opening doors to careers in space exploration and research.

Common Mistakes

MISTAKE: Thinking heavier objects fall faster than lighter objects in free fall. | CORRECTION: In true free fall (without air resistance), all objects accelerate at the same rate, meaning they fall at the same speed and cover the same distance in the same time.

MISTAKE: Forgetting that the initial velocity (u) is zero when an object is 'dropped' or 'released' from rest. | CORRECTION: If an object is simply dropped, its starting speed is 0 m/s. Only if it's 'thrown downwards' would it have an initial velocity.

MISTAKE: Confusing acceleration due to gravity (g) with the speed of an object. | CORRECTION: 'g' is the rate at which an object's speed increases each second (acceleration), not its actual speed at any given moment.

Practice Questions

Try It Yourself

QUESTION: A coin is dropped from a height of 20 meters. How long will it take to reach the ground if air resistance is ignored? (g = 10 m/s^2) | ANSWER: 2 seconds

QUESTION: An apple falls from a tree and takes 1.5 seconds to hit the ground. What was the height of the tree? (Ignore air resistance, g = 10 m/s^2) | ANSWER: 11.25 meters

QUESTION: A ball is thrown downwards from a 30-meter tall building with an initial speed of 5 m/s. How long will it take to hit the ground? (g = 10 m/s^2) | ANSWER: 2 seconds

MCQ

Quick Quiz

Which of the following scenarios best describes an object in free fall?

A feather falling slowly to the ground.

A kite flying high in the sky.

A stone dropped from a great height on the Moon.

A car speeding up on a highway.

The Correct Answer Is:

Option C is correct because on the Moon, there is no atmosphere, so a stone dropped there would experience true free fall, with only gravity acting on it. A feather on Earth (A) experiences significant air resistance, and a kite (B) and car (D) have other forces besides gravity acting on them.

Real World Connection

In the Real World

ISRO scientists use the principles of free fall to calculate the exact launch trajectories for satellites and rockets. When a rocket engine shuts off in space, the spacecraft effectively enters a state of free fall around Earth, allowing scientists to predict its orbit and ensure it reaches its destination accurately.

Key Vocabulary

Key Terms

GRAVITY: The force that attracts objects towards each other, especially towards the center of the Earth. | ACCELERATION DUE TO GRAVITY (g): The rate at which objects accelerate downwards due to Earth's gravity, approximately 9.8 m/s^2 on Earth. | AIR RESISTANCE: The force that opposes the motion of an object through the air. | VACUUM: A space entirely devoid of matter.

What's Next

What to Learn Next

Now that you understand free fall, you're ready to explore 'Projectile Motion'. This next concept builds on free fall by adding a horizontal motion component, helping you understand how things like cricket balls or javelins fly through the air!