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Newton’s Laws.

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Presentation on theme: "Newton’s Laws."— Presentation transcript:

1 Newton’s Laws

2 Sir Isaac newton Newton “Father of modern science”
https://www.youtube.com/watch?v=danYFxGnFxQ (My Man, Sir Isaac Newton) 1:58 min https://www.youtube.com/watch?v=UuFAfD7Krhk (biography Isaac Newton) 1:30 min For more info on Newton

3 Who was newton? an English physicist and mathematician who is widely regarded as one of the most influential scientists of all time and as a key figure in the scientific revolution laid the foundations for most of classical mechanics formulated the laws of motion and universal gravitation that dominated scientists' view of the physical universe for the next three centuries. He also demonstrated that the motion of objects on the Earth and that of celestial bodies could be described by the same principles.

4 First law or law of inertia
Why can’t expecting woman ride all the adventure rides at Universal? Why is a seatbelt a good idea? Why do I feel sick on a roller coaster? Predict what will happen next

5 1st law An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. There are two parts to this statement---one that predicts the behavior of stationary objects and the other that predicts the behavior of moving objects.

6 1st Law is same as law of inertia
What is inertia? an objects tendency to avoid change Property of matter History Notes: Newton's conception of inertia stood in direct opposition to more popular conceptions about motion. The dominant thought prior to Newton's day was that it was the natural tendency of objects to come to a rest position. The thought at the time was that moving objects would eventually stop moving; a force was necessary to keep an object moving. But if left to itself, a moving object would eventually come to rest and an object at rest would stay at rest

7 Critical application Fred spends most Sunday afternoons at rest on the sofa, watching pro football games and consuming large quantities of food. What effect (if any) does this practice have upon his inertia? Fred's inertia will increase! Fred will increase his mass if he makes a habit of this. And if his mass increases, then his inertia increases.

8 Critical application Ping pong vs bowling ball… both on a table.
Which is easier to move?

9 Critical application  Two bricks are resting on edge of the lab table. Shirley acquires an intense desire to know which of the two bricks are most massive. Since Shirley is vertically challenged, she is unable to reach high enough and lift the bricks; she can however reach high enough to give the bricks a push. Discuss how the process of pushing the bricks will allow Shirley to determine which of the two bricks is most massive. What difference will Shirley observe and how can this observation lead to the necessary conclusion? The bricks, like any object, possess inertia. That is, the bricks will resist changes in their state of motion. If Shirley gives them a push, then the bricks will offer resistance to this push. The one with the most mass will be the one with the most inertia. This will be the brick which offers the most resistance. This very method of detecting the mass of an object can be used on Earth as well as in locations where gravitational forces are negligible for bricks.

10 1st law But do some objects have more of a tendency to resist changes than others? Absolutely yes! The tendency of an object to resist changes in its state of motion varies with mass. Mass is that quantity that is solely dependent upon the inertia of an object. A more massive object has a greater tendency to resist changes in its state of motion

11 1st law Have you ever observed the behavior of coffee in a coffee cup filled to the rim while starting a car from rest or while bringing a car to rest from a state of motion? Coffee "keeps on doing what it is doing." When you accelerate a car from rest, the road provides an unbalanced force on the spinning wheels to push the car forward; yet the coffee (that was at rest) wants to stay at rest. While the car accelerates forward, the coffee remains in the same position; subsequently, the car accelerates out from under the coffee and the coffee spills in your lap. On the other hand, when braking from a state of motion the coffee continues forward with the same speed and in the same direction, ultimately hitting the windshield or the dash. Coffee in motion stays in motion.

12 Inertia Trick

13 2nd law Newton's second law of motion pertains to the behavior of objects for which all existing forces are not balanced. The second law states that the acceleration of an object is dependent upon two variables - the net force acting upon the object and the mass of the object. The acceleration of an object depends directly upon the net force acting upon the object, and inversely upon the mass of the object. As the force acting upon an object is increased, the acceleration of the object is increased. As the mass of an object is increased, the acceleration of the object is decreased.

14 2nd law

15 2nd law The acceleration is directly proportional to the net force
the net force equals mass times acceleration the acceleration in the same direction as the net force an acceleration is produced by a net force. The NET FORCE. It is important to remember this distinction. Do not use the value of merely "any 'ole force" in the above equation. Fnet=ma

16 2nd law Example problems:
What net force is required to accelerate a car at a rate of 2 m/s2 if the car has a mass of 3,000 kg? A10 kg bowling ball would require what force to accelerate down an alleyway at a rate of 3 m/s2? Sally has a car that accelerates at 5 m/s2. If the car has a mass of 1000 kg, how much force does the car produce? What is the mass of a falling rock if it produces a force of 147 N?

17 3rd law For every action there is an equal and opposite reaction
The statement means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the forces on the first object equals the size of the force on the second object. The direction of the force on the first object is opposite to the direction of the force on the second object. Forces always come in pairs - equal and opposite action-reaction force pairs.

18 3rd law A variety of action-reaction force pairs are evident in nature. Consider the propulsion of a fish through the water. A fish uses its fins to push water backwards. But a push on the water will only serve to accelerate the water. Since forces result from mutual interactions, the water must also be pushing the fish forwards, propelling the fish through the water. The size of the force on the water equals the size of the force on the fish; the direction of the force on the water (backwards) is opposite the direction of the force on the fish (forwards). For every action, there is an equal (in size) and opposite (in direction) reaction force. Action-reaction force pairs make it possible for fish to swim.

19 3rd law Consider the motion of a car on the way to school.
A car is equipped with wheels that spin. As the wheels spin, they grip the road and push the road backwards. Since forces result from mutual interactions, the road must also be pushing the wheels forward. The size of the force on the road equals the size of the force on the wheels (or car); the direction of the force on the road (backwards) is opposite the direction of the force on the wheels (forwards). For every action, there is an equal (in size) and opposite (in direction) reaction. Action-reaction force pairs make it possible for cars to move along a roadway surface.

20 Recap of newton’s laws Mythbusters and flying flight attendant
Identify how all three laws are in action in the clip WRITE THESE DOWN!!! https://www.youtube.com/watch?v=peZ7wZ5JXRE


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