Projectile motion refers to a trajectory motion (motion in a curved path) under the influence of gravitational force.

Examples of projectile motion include:
- Motion of football in the air
- Firing a cannon
- Water escaping from a hose
- Javelin throw

In projectile motion, the velocity in the horizontal direction and the acceleration in the vertical direction are constant.

The only force acting on a projectile is the force of gravity and therefore the acceleration of the projectile (a) is equal to the acceleration of freefall (g).

While solving problems related to projectile motion, the horizontal and vertical components should be dealt with separately.
- Trigonometric functions can be used to determine the components.
- In the case of direction, for the horizontal component, the right side is considered positive and the left side is considered negative. For the vertical component, the upward direction is considered positive and the downward direction is considered as negative. The positive and negative sides for the direction can be interchanged as well.
Projectile motion of a ball travelling from ground level and landing at ground level
- The velocity component can be resolved into the two components as shown below.
- The only force acting during the motion is the weight; therefore, the vertical acceleration is equal to the acceleration due to gravity (9.81 ms^-2 for Earth acting downwards) and the horizontal acceleration is 0 ms^-2.
- At the maximum height, the vertical velocity is 0 ms^-1 and the resultant velocity is equal to the horizontal velocity.
Some important graphs for the projectile motion of the football in the air are shown below:

Displacement-time graph
- The horizontal displacement is a straight line with a constant slope, as its gradient should represent a constant velocity.
- The vertical displacement will be a curve similar to the trajectory motion itself.
  
  Velocity-time graph
- The horizontal velocity is constant throughout the motion, and therefore the velocity line is parallel to the time axis.
- The vertical velocity decreases and becomes zero at the maximum height and starts increasing in the negative direction.
  
  Acceleration-time graph
- The horizontal acceleration is zero and the line overlaps the time axis.
- The vertical acceleration is constant and is equal to the negative acceleration of freefall.
Projectile motion of an object projected horizontally from a certain height
Some important graphs for the projectile motion of an object projected horizontally from a certain height:

Displacement-time graph
- The horizontal displacement is a straight line with a constant slope, as its gradient should represent a constant velocity.
- The vertical displacement will be a decreasing curve and becomes zero when the object lands on the ground.
  
  Velocity-time graph
- The horizontal velocity is constant; however, the vertical velocity increases in the downward direction (negative direction).
  
  Acceleration-time graph
- The horizontal acceleration is zero and the line overlaps the time axis.
- The vertical acceleration is constant and is equal to the negative acceleration of freefall.

2.03 - Projectile Motion

Learn Step-By-Step Video Explanation For This Topic

Explore our Revision Resources

Mock Exams

Tutor Support

Create an account