Everywhere you look you will see objects either sitting still or moving. We are so used to seeing these things, that you can probably make predictions about the motion of objects with ease. What you might not realize is that when you make these observations and predictions, you are actually observing and applying Newton's Laws of Motion.
Before we jump into Newton's Laws, we should discuss a foundational concept: forces. A force is a push or pull that causes an object to move or change its speed, direction, or shape. These forces might be obvious, like when you toss a ball into the air or push down on your bike pedals (applied forces). However, there are some forces that are harder to visualize, like the air resistance that objects experience as they fly through the air (frictional forces). Additional examples of forces are shown below. Contact forces are forces that rely on objects physically touching each other (direct contact), while non-contact forces don't rely on objects touching one another.
When you add up all the forces acting on an object, you are calculating the net force. If the net force is zero, that means the forces are balanced (equal in size and opposite in direction). This doesn't necessarily mean the object isn't moving though. Objects with balanced forces don't experience a change in motion, so if they are sitting still, they will continue to sit still, but if they are moving, they will continue to move at the same velocity. If the net force on an object is not zero, that means the forces are unbalanced (not equal and opposite). If this is the case, the object will experience a change in motion, meaning it will speed up, slow down, or simply change direction. See examples of balanced and unbalanced forces as well as force diagrams below.
Now that you know a little bit about forces, let's look at Newton's Laws of Motion.
1. Newton's first law is known as the Law of Inertia. This law states that an object at rest will remain at rest, and an object in motion will stay in motion, unless acted on by an unbalance force.
2. Newton's second law is known as the Law of Acceleration, and is best summarized with the equation F = m x a (force = mass times acceleration). Basically, this law states that the more massive an object is, the more force you will need to apply in order to cause the object to accelerate (speed up, slow down, or change direction).
3. Newton's third law is known as the Law of Action-Reaction. This law states that for every action, there is an equal and opposite reaction. For example, if you a kayaking or skateboarding, you push backwards (with your paddle or foot), but propel forwards.
Hopefully Newton's Laws of Motion are starting to make sense to you. Just to be sure though, try one or more of the experiments described below. You should be able to explain how Newton's laws apply to the experiment. If not, it might be good to review some more using one or more of the following websites.
Experiment #1. Table Cloth Trick
You have probably seen videos of people pulling a tablecloth off a table without knocking any dishes off, right? Well, now is your chance to do it too! Watch the video below and try it yourself. You may want to start with things that don't break though, just in case. When you are finished, make sure you can answer the following questions.
1. Which of Newton's laws are you modeling with this experiment?
2. Why don't the dishes go flying off the table with the table cloth?
3. Explain how you are modeling Newton's law(s).
Experiment #2. Egg Drop Trick
If you are interested in the table cloth trick, but want to start a little smaller, the egg drop trick is perfect for you. Watch the video below and try it yourself. When you are finished, make sure you can answer the following questions.
1. Which of Newton's laws are you modeling with this experiment?
2. Why does the egg land in the water instead of on the counter?
3. Explain how you are modeling Newton's law(s).
Experiment #3. Balloon Rocket/Car
Depending on what materials you have at home, you can create a simple balloon rocket (using just a straw, string, balloon, and tape), or a more complex balloon-powered car. Choose which one you are interested in making and watch the video below. Feel free to modify the experiment as needed. For example, if you already have a toy car, you could use that instead of building your own, or you could use a water bottle to make your car instead of cardboard. Additional examples of how to build cars can be found on the Mini-Racers webpage. When you are finished, make sure you can answer the following questions.
1. Which of Newton's laws are you modeling with this experiment?
2. Why does the car move forward? Why does it eventually stop moving?
3. Explain how you are modeling Newton's law(s).
Experiment #4. Centripetal Force Board
If someone held a glass of water over your head and tipped it upside down, the water would spill all over you. Hopefully you know which force is responsible for this by now. Can you think of a way to use the laws of physics to get the water to stay in the glass instead of spilling all over you? Try this centripetal force board activity to see if this is even possible! If you don't have the materials to make the board, you could try just swinging a bucket of water over your head instead. When you are finished, make sure you can answer the following questions.
1. Which of Newton's laws are you modeling with this experiment?
2. Why doesn't the water spill all over you?
3. Explain how you are modeling Newton's law(s).
If you want an explanation of centripetal force, you can watch Planet Nutshell's Centripetal Force video.
Experiment #5. Forces & Motion PHET Simulation
This PhET Simulation includes four different sections. Choose one or more of the sections and play around with it for awhile. When you are finished, make sure you can answer the questions for the section(s) you chose.
Net Force
1. How did you get the cart to start moving? Can you draw a force diagram?
2. How can you make it so one team wins with a net force greater than zero? How can you make one team win with a net force of zero?
3. What has to happen in order for the cart to accelerate (change speed or direction)? Reference the forces.
Motion
1. If you apply 500N of force, how long does it take different objects (1 crate, 2 crates, refrigerator, etc.) to reach the maximum speed?
2. Explain how mass affects the amount of time it takes to reach the maximum speed if the same force is applied.
3. Explain how mass affects the amount of force required to move an object.
Friction
1. What happens to an object on a surface with some friction when you consistently apply a force?
2. What happens to an object on a surface with some friction when you apply a force for a few seconds and then stop?
3. What happens to an object on a surface without friction when you apply a force for a few seconds and then stop?
Acceleration
1. How do you make the box speed up?
2. How do you make the box move at a constant speed?
3. How do you make the box stop? How do you make it change direction?
Bonus
Use these Newton's Laws handouts to test your understanding. There are a variety of handouts, ranging from vocabulary checks to word searches and crosswords, so choose the ones that look the most interesting.