Idea 2of 5Builds onTwo motions at once
Across is steady
What happens to the sideways motion?
Today you'll discover
- equal steps across, every frame
- why nothing slows the sideways motion
- the first of the two equations
Think firstThe fired ball, frame by frame
Look at the ball's steps across. Are they equal, growing, or shrinking?
Decide first, then press Next. Count the marks along the top.
The fired ball alone, with its earlier positions ghosted along a curve. After a prediction, marks along the top show the ball's steps across, evenly spaced, each 0.48 metres every 0.16 seconds. The last step shows a cliff launch and asks how far out the ball lands.
See the whole ideathe big idea and the key word, in one place
The big idea
Across: steady. Distance across is speed times time.
Why it happensGravity pulls straight down. It has no sideways part, so it cannot change the sideways motion at all.
Key word
- horizontal
- the sideways part of a projectile's motion: steady velocity, no acceleration
About this modelAir is ignored: the ball is drawn as it would move in a vacuum.
Air is ignored: the ball is drawn as it would move in a vacuum.
Ready to use it?
- Find how far out a projectile lands from its speed and time.