You know a little about how things move, right?  Great, I could use your help.  Here's what's happening.  Out in Africa, there are some scientists who need to get some elephant poop for their studies.  We need you to float in this helicopter above them and watch the elephants to make sure they do not run over the scientists.  Watch for when the elephants speed up, when they change direction, and when they keep going in the same speed and direction.  Do not worry.  You will do great.


Ready to go up in the helicopter?  Great.  Chop chop chop chop chop.  Now the scientists are below you.  It looks like the elephants are coming right at them.  The elephants are moving pretty slowly though.  Uh-oh.  Now it looks like they are speeding up.  Acceleration is when something speeds up, slows down, OR changes direction.  This means it has to keep going faster and faster or slower and slower.  The elephants are now covering more ground in a shorter amount of time than they were a little while ago.  Should you land the helicopter and grab the scientists?

OK everybody, follow me.

USAID Africa Bureau, Public domain, via Wikimedia Commons

Not so fast.  It looks like the head elephant is accelerating again.  This time he's slowing down and turning.  Velocity means how fast something is moving as well as what way it's pointed.  When something accelerates, there is always a change in velocity, which can be a change in either speed or direction.  Right now the elephants are headed toward a bush and eating some leaves.  Once they finish, are they going to speed up again?

Yum, tree leaves for breakfast again.

Chadica, CC BY 2.0 , via Wikimedia Commons

Sure enough, once the elephants stop eating, they head right back toward our scientists.  Luckily for us, the food seems to have slowed them down.  This time they do not go faster and faster.  They also do not go slower and slower.  To maintain means to keep the same.  If the elephants keep moving at a slow speed, they maintain a slow speed.  Still, even at this pace, they are getting closer.


Oh, great.  The elephants are speeding up again.  The scientists still do not have what they need.  They are not too far away now, only one football field, so you really need to know your stuff.  How can you let the scientists know how fast the elephants are moving?  How long do the scientists have?  We can measure how much something speeds up or slows down over time (how much it accelerates) in m/s2, which means meters per second squared.  By watching your clock and looking at how much the elephants are speeding up, you can tell how quickly they will reach our scientists.  They're about thirty seconds away.  We had better land and grab them.

Do you see any scientists? I don't see any scientists.

Photo: SAC Phil Major RAF/MOD, OGL v1.0OGL v1.0, via Wikimedia Commons

Just as the helicopter touches down, the scientists found the poop they were looking for.  Yes!  Because you knew all about how things speed up and slow down, you could see where the elephants would be and when.  You could get a pretty good idea of when they would reach the scientists.  And I will bet you could do it again.  As you lift off, the elephants come in.  And all they run over are the scientists' prints, and not the scientists.


References:

Physics 4 Kids.  "Velocity, Speed, and Motion . . . Oh My!"  Physics 4 Kids, 2009.  <http://www.physics4kids.com/files/motion_velocity.html>