Idea 3of 5Builds onAcross is steady
Down is free fall
What happens to the downward motion?
Today you'll discover
- drops that grow every frame
- why the fired ball drops like the dropped one
- the second of the two equations
Think firstNow the drops, frame by frame
Look at how far the balls drop in each step. Equal, growing, or shrinking?
Decide first, then press Next. Compare the brackets down the right-hand side.
Both balls, frame by frame, with brackets down the right-hand side measuring each drop: 0.13, 0.38 and 0.63 metres, growing. After a prediction, a dashed line shows the two balls level at each moment, then both land together. The last step asks about the acceleration at the top of a thrown ball's arc.
See the whole ideathe big idea and the key word, in one place
The big idea
Down: free fall. Both speed up by 9.8 m/s each second.
Easy to get wrongAt the top of an arc the vertical velocity is zero for an instant. The acceleration is still 9.8 m/s² down; that is what brings it back.
Key words
- free fall
- motion under gravity alone: uniform acceleration of 9.8 m/s² downward, near Earth's surface
- vertical
- the up-and-down part of a projectile's motion: free fall, starting from whatever vertical velocity it was given
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 a projectile falls in a given time.