Projectile Motion and Trajectory

You’ve Been Watching it for Years

Projectiles are objects moving through space or the air with their own inertia and

acted on by gravity.

Projectiles have a horizontal or X motion.

Gravity does not act in the X direction.

If there is no friction the x motion is at constant

velocity.

Projectiles have a vertical or y motion.

Velocity in the y direction will accelerate because of

gravity.

Because acceleration

due to gravity is constant a projectile and

free-falling object will hit the ground at

the same time!

The projectile will travel in a parabola, the combination of the

x and y motion.

Upwardly Launched Projectiles

In the absence of gravity the projectile flies in a straight line!

Gravity pulls the projectile down as if it has been free-falling from

each point!

If there is no air resistance the horizontal or x velocity

stays constant!

Notice the vertical or y velocity decreases as the projectile goes upwards!

Yet the vertical or y velocity increases as the projectile

goes downwards!

Why?

The vertical speed of the cannonball lost going upwards……

50 m/s

30 m/s

10 m/s 10

m/s30 m/s

50 m/s

Equals the vertical speed of the

cannonball gained going

downwards……

50 m/s

30 m/s

10 m/s 10

m/s30 m/s

50 m/s

What is the vertical speed of the

cannonball at the top of the parabola?

0 m/s

What about air resistance?

No air resistance

With air resistance

Air resistance causes the

trajectory to be less than the ideal path!

Force of LaunchA projectile launched with more force will go further than one launched with less force if all other factors are the

same….

Does Angle of Launch Matter?

Yes!

45° gives maximum distance or range! (x and y are equal)

Any two angles which add up to 90° gives the same distance or

range but not the same trajectory!

75° + 15° = 90°

60° + 30° = 90°

Is an airplane a projectile?

No! It is not moving on its own inertia but by constant thrust

from the jet engines!

With the right amount of force a projectile will fall at the same rate

as the Earth’s surface curves!

Satellites need to have a velocity of 8 km/s to stay in

orbit.

Satellites do not escape the Earth’s gravity but orbit above

the atmosphere. Why?

Once they escape the atmosphere there is no friction

so velocity is constant!

The End