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Overview of Newton's Laws

Overview of Newton's Laws

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Author: David Vetter
Description:

A brief overview of Newton's Laws.

Standards:

Newton’s second law accurately predicts changes in the motion of macroscopic objects. (HS-PS2-1) 


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Tutorial

Newton's Three Laws

The short version of Newton's three laws are:

1. Objects in motion stay in motion and objects at rest stay at rest unless acted upon by unbalanced forces.

2. The magnitude of a force is equal to the mass of an object times the magnitude of its acceleration. In other words, F=ma.

3. For every action there is an equal and opposite reaction.

Let's take a look at each individually.

Newton's First Law: Inertia

Newton's First Law is very straightforward:

1. If an object is not moving, something has to interact with it (exert a force on it) to make it move. Otherwise, it will continue to sit there.

2. If an object is already moving, something has to interact with it (again, exert a force on it) to make it move. Otherwise, it will keep going at the same speed in the same direction.

Newton's First Law of Motion - Science of NFL

Source: National Science Foundation. (2015, January 27). Newton's First Law of Motion - Science of NFL Football. Retrieved May 09, 2016, from https://www.youtube.com/watch?v=08BFCZJDn9w

Newton's Second Law: Definition of Force

With Newton's Second Law we define the effects of a force.

A force will cause an object to accelerate based on its mass.

In other words:

F equals m a

However, it's rare that only one force is acting on an object at a time. So we're going to amend this by using the Greek letter Sigma, which in Math and Physics means "Sum of".

sum F equals m a

In other words, the sum of the forces acting on a mass will cause it to accelerate. We'll see why we use this form soon.

Newton's Second Law of Motion - Science of NFL Football

Source: National Science Foundation. (2015, January 28). Newton's Second Law of Motion - Science of NFL Football. Retrieved May 09, 2016, from https://www.youtube.com/watch?v=qu_P4lbmV_I

Newton's Third Law of Motion: Equal and Opposite

This law is a little stranger to summarize, so I'll let the video do it and then come back.

Newton's Third Law of Motion - Science of NFL Football

Source: National Science Foundation. (2015, January 29). Newton's Third Law of Motion - Science of NFL Football. Retrieved May 09, 2016, from https://www.youtube.com/watch?v=e1lzB36aHD4

Newton's Third Law: continued

The video mentioned two important things:

1. Equal and opposite reactions

2. Conservation of Momentum

We'll study Conservation of Momentum more soon, but I wanted to include it here because it helps with the other idea.

A gentleman in the video mentions that if I push on an object, it pushes back. This seems odd, but it's really important. If I push on a ball, that ball resists moving (thanks to Newton's First Law). I can feel that resistance when I push on it. If I push something larger, like a cooler full of ice, I'll notice it more.

After the quiz:

Once you've completed the quiz, follow this link to a longer question. Think carefully about it and use the answers you've gotten here to help.

Big Think question