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Using the Automobile to Understand Newton's Laws of Motion

Sir Isaac Newton thought of his three laws of motion hundreds of years ago, but his formulas are still used daily by physicists around the globe. His three, simple laws can explain, more or less, all movement in the entire universe! Understanding them can be difficult, as they sometimes can include complicated equations and terminology, so we are going to use the basic movements of cars as an example. Use the examples and the resources below to learn about Newton's Three Laws of Motion.

Newton's First Law

An object in motion tends to stay in motion. An object at rest tends to stay at rest. This is unless the object is acted upon by an unbalanced force.

This first law is referred to as the "law of inertia". If you think about this, logically it is very simple and very true. What a mad universe we would live it if things moved with no rhyme or reason! We wouldn't be able to throw a ball, dance, or drive a car.

Newton's idea of forces included balanced forces and unbalanced forces. Balanced forces include equal forces pushing in opposite direction – which equals out to be no force. Just as in a game of tug-of-war, if two groups are pulling the rope with the exact same amount of force, then the little flag in the middle would not move at all. An unbalanced force, however, features a force in one particular direction, which causes the object to accelerate or decelerate.

A car is a bit of matter, an object, which likes to stay at rest. It won't move if it's not on. A great deal of minor explosions happen inside the engine in order for it to go. It doesn't simply start moving by itself, but forces created in the engine propel the car forward. This is why cars require energy sources, like electricity, gasoline, or diesel in order for them to move.

Newton's Second Law

The acceleration is proportional to the force on an object, and inversely proportional to its mass.

Newton's second law is often represented by the equation F=ma, where "F" refers to force, "m" refers to mass, and "a" refers to acceleration. Acceleration can also be referred to as the change in velocity divided by time. Before being overwhelmed by how strange those words sound, realize that Newton's Second Law of Motion is something you already see in real life every day. The more mass an object has, the more force is required to accelerated it.

Let's say a car runs out of gas, and we need to push it about a yard. A small sports car will need one or two people to push it in order for it to move. On the other hand, what if we needed to move a big eighteen-wheel truck? A lot of people would need to push very hard to move it, and it probably wouldn't move very much at all. We would need a greater amount of force to move the larger mass the same distance.

Newton's Third Law

For every action there is an equal and opposite reaction.

People sometimes use this phrase in day-to-day life without referring to physics. However, what this law means is that two equal forces happen at the same time, and at opposite directions. These forces don't cancel out because they happen on different objects.

The perfect, and unfortunate, example of this is a car accident. Two cars, a green car and a red car, gently bump into each other in a parking lot. The red car was moving and the green car was parked. When they collide, one might think that only the red car was exuding a force, which caused the impact on the green car, but the green car was also pushing back with an equal and opposite force on the red car, which caused it to stop. In this way, forces occur in pairs.

Activities and Lesson Plans

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