# Projectile motion

Motion of a thrown object under gravity alone. Sideways speed stays constant while up-and-down motion has acceleration g.

Physics (university) · Part 01: Motion and vectors · Card 7 of 8 · Last updated 2026-10-19

## Analogy

Two separate movies played together: one steady, one speeding up downward.

## Example

**Kicked ball**

Time = 2(20 sin 30)/9.8 = 2.04 s
Range = 20 cos 30 x 2.04
Range = 35.4 m

## In practice

A ball kicked at 20 m/s and 30 degrees lands about 35 m away.

## Practice

### Flashcards

- **What stays constant in projectile motion, ignoring air?** The horizontal velocity.

### Interview questions

**A projectile is launched at 30 m/s at 40 degrees above flat ground. Explain how to find its time of flight and range.**

- Split velocity into components
- Vertical motion uses g to find time up and down
- Horizontal speed is constant, so range is that speed times time

## Questions people ask

### What launch angle gives the longest range?

On level ground with no air, 45 degrees gives the longest range. At 45 degrees the launch speed splits evenly between rising and travelling forward. Angles that add up to 90 degrees, like 30 and 60, give the same range, although the higher one stays in the air longer.

### Does air resistance matter in projectile problems?

In real life yes, but most first-year problems ignore it so the maths stays simple. Air drag shortens the range and makes the path steeper on the way down. A heavy, smooth ball like a shot put follows the ideal path closely, while a badminton shuttle does not.

## Related concepts

- [Vector components](https://studyvisually.com/learn/science/physics-university/physics-university-part-1/physics-university-part-1-concept-6)
- [Relative velocity](https://studyvisually.com/learn/science/physics-university/physics-university-part-1/physics-university-part-1-concept-8)

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