A.1 · IB Physics
Projectile motion
Fire a projectile and change the launch angle, speed, height, gravity or air resistance. The horizontal and vertical motions stay independent, and the live components show it.
Predict first
Start from the default settings (45°, 22 m s⁻¹, Earth, no air resistance). Change Gravity to Moon. What happens to the range?
With no drag R = u²sin2θ ÷ g, so R ∝ 1/g. The ratio of g values is 9.8 ÷ 1.62 ≈ 6.05, so the range rises from about 49.4 m to about 299 m.
Check it in the model: Choose Moon in the Gravity list and compare the Range readout (49.4 m on Earth, 299 m on the Moon).
path vₓ vy previous / no-drag path
no drag: R = u cosθ · T
drag: a = −g ŷ − (c ÷ m) |v| × (velocity)
Try this
- Keep air resistance off and launch at 30°, 45° and 60° with the same speed. Which two angles give the same range, and which gives the greatest?
- Choose the Moon, then Earth, at 45° and 22 m s⁻¹. Compare the range, maximum height and time of flight: which quantities scale with 1/g?
- Tick Air resistance and raise Mass from 2.0 to 10.0 kg with everything else fixed. Why does the path move towards the dashed no-drag curve?
Exam tip: Treat x and y separately (constant vₓ, vertical acceleration −g), state the value of g you use, and give the answer to a sensible number of significant figures; with air resistance the best angle falls below 45° and the path is no longer symmetric.