A catapult is a ballistic device used to launch a projectile a great distance without the aid of gunpowder or other propellants.

A catapult uses the sudden release of stored potential energy to propel its payload.

Parts of a Catapult

• Bucket – a container use to hold the payload prior to release;
• Payload – the object that will be discharge in projectile motion;
• Arm – holds the Bucket that has a pivot connection at the base;
• Base and Frame – Supports the Catapult’s weight and action;
• Rope – stores potential energy by stretching or winding up while it is attached directly or indirectly to the arm;
• Restraining Rope – it serves as the trigger of the catapult once release;
• Counterweight – used in other type of catapult. Stores potential energy by setting it in a higher elevation and drop it once the restraining rope is released.

Energies involved in the catapult’s mechanism

There are three primary energy storage mechanism used in a catapult.

• Tension – is built by stretching the rope up to the maximum limit. When it is stretched, the potential energy stores in the rope, parallel to the direction of how it is stretched.
• Torsion -is built in the pivot point of the arm. the more you twist the rope, the greater energy you stored tangent to the center of rotation.
• Gravity – counterweight is one type of storing the potential energy by pulling a heavy object against the gravitational force.

Once the Payload is released in the Catapult, it will create a projectile motion towards the direction it is positioned.

Effect of Velocity in a Projectile Motion

Velocity is the distance travelled of an object over time. In a projectile motion, it affects the distance travelled of an object. The higher the velocity, the farther it can reach at the same angle.

To show you the effect, in image 2, we have a cannonball weighing 20kg that is shot at an angle of 45 degrees.

Effect of Angle in a Projectile Motion

Angle affects how far and how high the object will go in a projectile motion.

Using the simplified formula: R = (Vo2sin2Ø)/g

• R – Range
• Vo – Initial Velocity of the Object
• Ø – Angle of discharge in a projectile motion
• G – Gravitational force

We can compute for the maximum distance traveled.

Here are the samples images with same object and initial velocity but differs in the angle.

Do you see the changes in distance and height travelled by the cannonball at different angles?

At 45 Degrees, the vertical and horizontal forces are equal giving the cannonball the farthest distance it can reach at a given velocity and gravitational force.

While at 90 degrees, the cannonball can attain the maximum elevation it can reach at a same velocity and gravitational force

Effect of Gravity in a Projectile Motion

Every planet has its own gravitational pull. Here on earth, our gravitational pull is 9.807m/s², while on the moon it is 1.62m/s². This force is pulling the object towards the center of the planet. In a projectile motion, it affects the time an object will hit the ground, the distance it will travel, and the maximum height it can achieve.

In image No. 9, it shows changing the value of gravity in a 20kg cannonball that fires at 20m/s velocity at 45-degree angle.

The lower the gravitational pull, the farther the object can travel at a given instance.

You may also check https://phet.colorado.edu/sims/html/projectile-motion/latest/projectile-motion_en.html for you to explore more about projectile motion by varying the gravitational force and including Air resistance of the object.

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