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Newton’s Laws of Motion

Clip Art Credit: Phillip Martin

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Background

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Sir Isaac Newton (1643-1727) an English scientist and mathematician famous for his discovery of the law of gravity also discovered the three laws of motion. Today these laws are known as Newton’s Laws of Motion and describe the motion of all objects on the scale we experience in our everyday lives.

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Sir Isaac Newton

“If I have seen further it is by standing on the shoulders of giants”

  • Isaac Newton

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Newton’s 1st Law of Motion

An object at rest tends to stay at rest and an object in motion tends to stay in motion at constant velocity unless acted upon by an unbalanced force.

What happens to the driver when they hit the brakes? Why??

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Image Source: Boundless. “The First Law: Inertia.” Boundless Physics. Boundless, 26 May. 2016. https://www.boundless.com/

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What does the 1st Law mean?

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  • An object will keep doing what it is doing unless acted upon by an unbalanced force
  • An object at rest will remain at rest
  • An object in motion will remain in motion
  • If the forces are balanced, there is no change in motion, and therefore, no ACCELERATION!!

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What is meant by unbalanced forces?

If the forces on an object are equal and opposite, they are said to be balanced, and the object experiences no change in motion. If they are not equal and opposite, then the forces are unbalanced and the motion of the object changes.

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Think TUG-OF-WAR.

Image Source: Tug-of-War. Digital image. TutorCircle. N.p., 20114. Web. <http://physics.tutorcircle.com/forces/unbalanced-force.html>.

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Newton’s 2nd Law of Motion

Force equals mass multiplied by acceleration.

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F=m*a

Image Source: http://www.decaturisd.us/

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What does the 2nd Law mean?

  • Force is DIRECTLY proportional to acceleration.
  • The greater the force, the greater the acceleration.
  • The smaller the force, the smaller the acceleration.
  • Mass is INVERSELY proportional to acceleration.
  • The greater the mass, the smaller the acceleration.
  • The smaller the mass, the greater the acceleration.

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Newton’s 3rd Law of Motion

For every action there is an equal and opposite reaction.

What happens when you step off a boat?

Image Source: Boat Action-Reaction. Digital image. Web. 21 June 2016. <http://www.wired.com/2013/10/a-closer-look-at-newtons-third-law/>.

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What does the 3rd Law mean?

For every force acting on an object, there is an equal force acting in the opposite direction. Right now, gravity is pulling you down in your seat, but Newton’s Third Law says your seat is pushing up against you with equal force. This is why you are not moving. There is a balanced force acting on you– gravity pulling down, your seat pushing up.

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Conclusion

This video provides a nice summary of Newton’s Laws of Motion!

Video Source: Bryaneye. "VideoBrief: Newton's Laws of Motion Illustrated with 3D Animations and Motion Graphics." YouTube. YouTube, 30 Aug. 2008. Web. 21 June 2016. <https://www.youtube.com/watch?v=iH48Lc7wq0U>.