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What is a Projectile (physics)?
Grade Level:
Class 8
Space Technology, EVs, Climate Change, Biotechnology, HealthTech, Robotics, Chemistry, Physics
Definition
What is it?
A projectile is any object that is thrown, shot, or launched into the air and then moves only under the influence of gravity. It follows a curved path called a trajectory. Examples include a cricket ball hit by a batsman or a stone thrown from a catapult.
Simple Example
Quick Example
Imagine you are playing cricket and hit a six! The cricket ball flies high into the air, goes over the boundary, and lands. Once the bat hits it, the ball becomes a projectile, meaning only gravity pulls it downwards while it's moving through the air.
Worked Example
Step-by-Step
Let's say a boy throws a small stone horizontally from the top of a 20-meter tall building. We want to understand its motion.
1. The stone is launched horizontally, so its initial vertical speed is 0 m/s.
---2. Gravity will immediately start pulling the stone downwards, making its vertical speed increase.
---3. The horizontal speed of the stone, ignoring air resistance, will remain constant throughout its flight.
---4. The stone will follow a curved path, eventually hitting the ground.
---5. Its motion can be broken down into two independent parts: constant horizontal motion and vertically accelerated motion due to gravity.
---6. This stone, once thrown, is a projectile.
Why It Matters
Understanding projectiles is crucial for designing rockets and satellites at ISRO, predicting the path of a drone delivering packages, or even making sure a football reaches its target. Engineers, sports scientists, and even defense personnel use this knowledge to develop amazing technologies and strategies.
Common Mistakes
MISTAKE: Thinking a projectile's horizontal speed changes after being launched. | CORRECTION: Assuming no air resistance, the horizontal speed of a projectile remains constant throughout its flight. Only gravity affects its vertical motion.
MISTAKE: Believing that a projectile needs a constant 'push' to keep moving forward in the air. | CORRECTION: Once launched, a projectile moves due to its initial momentum and gravity. No continuous force is needed to keep it moving horizontally.
MISTAKE: Confusing the initial launch force with the forces acting during the flight. | CORRECTION: The launch force only acts for a very short time. Once the object is free, the only significant force acting on a projectile (ignoring air resistance) is gravity, pulling it downwards.
Practice Questions
Try It Yourself
QUESTION: Is a rocket still a projectile when its engines are firing? | ANSWER: No, because its engines are providing an upward thrust, meaning it's not moving only under the influence of gravity.
QUESTION: A javelin is thrown by an athlete. What forces act on the javelin after it leaves the athlete's hand (ignoring air resistance)? | ANSWER: Only the force of gravity acts on the javelin, pulling it downwards.
QUESTION: If you drop a cricket ball and simultaneously throw another cricket ball horizontally from the same height, which one hits the ground first? | ANSWER: Both will hit the ground at the same time, because gravity acts on both equally, making their vertical motion identical.
MCQ
Quick Quiz
Which of the following is NOT an example of a projectile?
A basketball shot towards the hoop
A stone thrown into a pond
A car driving on a straight road
A bullet fired from a gun
The Correct Answer Is:
C
A car driving on a straight road is not a projectile because it is supported by the road and propelled by its engine, not moving freely under gravity. The other options are objects launched into the air, moving only under gravity.
Real World Connection
In the Real World
Projectile motion is key in sports like cricket, football, and kabaddi. When a bowler bowls a bouncer, or a footballer takes a free kick, understanding the trajectory helps them aim. Even ISRO scientists use these principles to calculate the paths of rockets and satellites after launch.
Key Vocabulary
Key Terms
TRAJECTORY: The curved path an object follows when it's a projectile. | GRAVITY: The force that pulls objects towards the center of the Earth. | AIR RESISTANCE: The force that opposes the motion of an object through the air. | VELOCITY: The speed of an object in a specific direction.
What's Next
What to Learn Next
Great job learning about projectiles! Next, you can explore 'Factors Affecting Projectile Motion' like launch angle and initial speed. This will help you understand how to control a projectile's path and apply it to real-world problems.
