Before we get into Newton’s Second Law, we need to get up to speed with acceleration. In physics acceleration is defined as a change in velocity. In other words, it is a change in speed or a change in direction. It is how much time it takes something to go from one velocity to another.Remember that velocity is speed and direction. If you go straight ahead on your bike at a constant speed of 5 mph you are not accelerating. Neither your speed nor your direction is changing. Now, if you are stopped at a stop light and it turns green, you are accelerating as your speed increases from 0 mph to 10 mph.

The same thing happens if you are traveling at a nice even 10 mph and slow to a stop.In physics we don’t use the word deceleration. We use positive and negative acceleration. Now what happens if you are in a car and it turns a corner at a constant speed of 15 mph? Is it accelerating or not? Well, the speed is not changing but its direction is, so it is indeed accelerating.Remember back when we talked about gravity? We learned that gravity accelerates things at 32 feet per second². Now this may make a little more sense. Gravity made something continue to increase in speed so that after one second of having the force of gravity pull on something, that something has reached a speed of 32 feet per second. When that thing started falling it was at 0 velocity, after a second it’s at 32 feet per second after 2 seconds it’s at 64 feet per second and so on.It’s the old formula v = gt or velocity equals the gravitational constant (32 ft/s²) times time.
If something has an acceleration of 5 ft/s² how fast will it be going after 1 second…2 second…3 seconds? After one second it will be going 5 ft/s; after two seconds 10 ft/s; and after three seconds 15 ft/s. Again, it’s just like v = gt (v is velocity, g is the gravitational constant, t is time) but put the rate of acceleration of the object in place of g to get the formula v = at or velocity equals acceleration times time.

Scientific Concepts:

  • Acceleration is the rate of change in velocity. In other words, how fast is a change in speed and/or a change in direction happening.
  • Velocity is speed and direction.
  • A formula for acceleration can be a = (change in velocity)/time
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Special Science Teleclass: Physics of Motion
This is a recording of a recent live teleclass I did with thousands of kids from all over the world. I've included it here so you can participate and learn, too! We're going to cover energy and motion by building roller coasters and catapults! Kids build a working catapult while they learn about the physics …

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Driveway Races
This experiment is one of my favorites in this acceleration series, because it clearly shows you what acceleration looks like. The materials you need is are:
Gyro Wheel
Gyroscopes defy human intuition, common sense, and even appear to defy gravity. You'll find them in aircraft navigation instruments, games of Ultimate Frisbee, fast bicycles, street motorcycles
Downhill Race
Newton’s Second Law is one of the toughest of the laws to understand but it is very powerful. In its mathematical form, it is so simple, it’s elegant.
Rocket Car
Let's take a good look at Newton's Laws in motion while making something that flies off in both directions. This experiment will pop a cork out of a bottle and make the cork fly go 20 to 30 feet, while the vehicle moves in the other direction!
Newton’s Wagon
This is a quick and easy demonstration of how to teach Newton's laws with minimal fuss and materials. All you need is a wagon, a rock, and some friends.
G-Force
A common misconception in science is that centrifugal and centripetal force (or acceleration) are the same thing. These two terms constantly throw students into frenzy, mostly because there is no clear definition in most textbooks.
Balloon Racers
We're going to experiment with Newton's Third law by blowing up balloons and letting them rocket, race, and zoom all over the place. When you first blow up a balloon, you're pressurizing the inside of the balloon by adding more air (from your lungs) into the balloon.
Rocket Ball Launcher
This is a satisfyingly simple activity with surprising results. Take a tennis ball and place it on top of a basketball... then release both at the same time.
Impulse & Momentum
It’s time for the last lesson of mechanics. After all this time, you now have a good working knowledge of the rules that govern almost all movement on this planet and beyond!!