Newton’s Third Law states that:

To every action there is always an equal and opposite reaction: or the forces of two bodies on each other are always equal and are directed in opposite directions. (Wikipedia)

In a nutshell, for every action force, there is a reaction force with equal magnitude in the opposite direction. Newton’s third law can be observed every day in anyone’s life, however, many of us don’t realize this. One example is when we are walking. Our legs push down on the ground, the opposite reaction making us walk forward. There are so many examples that display Newton’s Third Law of Motion that I could go on forever.

However, the scenario that I think best exemplifies Newton’s Third Law is a car crash.

Luckily there’s nobody inside!

How does the third law relate to a car crash?

In a car crash, the action force(s) are the cars colliding with each other. The reaction force is the force sent back due to the collision, which is what causes the damage to the car. When two cars are headed straight at each other, they are travelling in opposing directions. When they finally collide, if they apply the same amount of force, they will experience a reaction of equal magnitude. This causes the destruction of the front of both cars. Since FORCE IS EQUAL TO MASS MULTIPLIED BY ACCELERATION (F = ma), a car with a much greater mass will likely do better or even survive in a car crash compared to a car with a smaller mass, even if the two vehicles were travelling at the same acceleration.

Before being released to the market, new car models must be tested in a crash facility. There, they undergo and must pass safety tests, which involve the infamous crash test dummy in a car speeding head on at a barrier. Here is a video of a crash test:

This video shows that as the car is speeding up toward the wall, it’s acceleration increases, while mass stays constant. This causes the total force to increase. When the car makes contact with the barrier, there is reaction of equal magnitude that arises from the car making contact with the barrier. The reaction force is easily visible in a car crash, which is why it is such a great way to show how Newton’s Third Law can be applied to our lives.

In what other ways do you think Newton’s Third Law can be shown in our everyday lives? Leave it in the comment section 🙂


Elert, G. (2012). Action-Reaction. Retrieved May 21, 2012, from

Newton’s laws of motion: Newton’s third law. (2012). Retrieved May 21 2012 from Wikipedia:’s_laws_of_motion#Newton.27s_third_law

Newton’s Third Law of Motion. (2012). Retrieved May 21 2012 from The Physics Classroom:

YouCarPress. (2012, February 22). 2012 BMW 1-Series CRASH TEST . Retrieved from