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## Newton’s Laws of Motion

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**Isaac Newton**(1642 – 1727) Newton’s Laws of Motion**What is a Force?**Force can be defined as a or a or anything else that has the ability to change motion.**In SI units, a force is measured in newtons (N). One newton**is about the amount of force it takes to lift a quarter-pound cheeseburger.**How do you figure force?**F = m • a Force= mass x acceleration Newton (N) (kg) (m/s2 ) Easier than saying kilogram m/sec2 newton**2 Kg Mass**To Understand Force… You must understand the difference between Mass Weight AND**What is Mass?**The amount of “matter” in an object. 1 Kg Mass 1.5 Kg Mass 2 Kg Mass Mass is measured in kilograms.**How is Mass Different Than Weight?**Weight is mass times the force of gravity Weight is a measurement of FORCE. 9.8 N 19.7 N 14.8 N (1 kg x 9.86 m/s2) F=ma (2 kg x 9.86 m/s2) (1.5 kg x 9.8 6m/s2) Acceleration due to gravity (9.8 m/s2) Acceleration due to gravity(9.8 m/s2) Acceleration due to gravity (9.8 m/s2) 1.0 Kg Mass 1.5 Kg Mass 2.0 Kg Mass How can you measure force? Calculate mass x acceleration.**100 Kg**Mass is 220 lbs Being pulled by different gravity? Your weight may be different. However, your mass never changes. On the Moon220 lbs.would weigh 35 lbs. On the Sun220 lbs.would weigh 5,956 lbs. On Mars220 lbs.would weigh 82.9 lbs. What’s “Your Weight On Other Worlds?” http://www.exploratorium.edu/ronh/weight/**Newton's Three Laws of Motion**Isaac Newton is the first scientist responsible for formulating laws regarding motion. These laws explain why objects move (or don't move). Let’s look at Newton's three laws of motion...**Newton's 3 Laws**An object will remain at rest unless acted upon by an “unbalanced” force. An object in motion will continue with constant speed and direction, unless acted on by an unbalanced force. 1 This law shows how force, mass and acceleration are related as shown in the equation below: Force = mass x acceleration 2 For every action force there is an equal and opposite reaction force. 3**Newton’s First Law: Balanced Forces**An object will maintain a constant state of motion. (Speed and direction remain unchanged) This means an object at rest tends to stay at rest and an object in motion continues in the same direction with the same speed. Balanced Forces This is known as Inertia Stay in motion: a bowling ball tossed in space Stay at rest: a book on a table It will go on and on forever. Table pushes up on book Science Gravity pulls down on book**Newton’s First Law: Unbalanced Forces**An unbalanced force is a force that changes the motion. In space there is no resistance to cause friction, so a bowling ball would stay in motion… The book below slides and then stops because of a resistant force called friction. Friction is force that opposes motion. unless another object got in the way Force of friction stops the book Science**What causes friction?**There are two factors which affect friction between two surfaces: • Kind of surfaces in contact (rough or smooth) • Amount of force pressing the surfaces together The rougher the surface and the stronger the force between the surfaces, the greater the amount of friction.**Of course “frictional” force happens on Earth...**but, if you weren’t wearing a safety belt you would continue your motion… Don’t let this happen to you! BUCKLE UP!!!!**There are 4 types of friction**1) Static friction: friction between two surfaces which are not moving past each other Example: trying to move a box and it will not move**There are 4 types of friction**2) Sliding friction: occurs when a force is great enough to overcome the static friction Example: two people create enough force to make the box move**There are 4 types of friction**3) Rolling friction: the friction which enables wheels to turn and objects to move**There are 4 types of friction**4) Fluid friction: occurs when an object moves through a gas or liquid**Let’s see how Newton’s First Law of Motion applies to**the NFL https://www.youtube.com/watch?v=08BFCZJDn9w 3:52**Newton’s Second Law: Force = Mass X Acceleration**Force and acceleration are related. 120 kg Lineman 100 kg Center F = ma F =ma Scenario # 1 Look at the situation above. If the acceleration 3 m/s2 from the snap was equal between these players, then who would have the advantage of force? Lineman = 3 m/s2 x 120 kg is 360 N Center = 3 m/s2 x 100 kg is 300 N The Lineman has the advantage. Scenario # 2Now, let’s say the Center has a 1 m/s2 advantage over his opponent at an acceleration of 4 m/s2 from the snap. Now who has the advantage of force? Lineman = 3 m/s2 x 120 kg is 360 N Center = 4 m/s2 x 100 kg is 400 N Now, the Center has the advantage.**Solving Force Problems**Step 1 Read the problem. Draw a picture. Step 2 Write down what you know. What are you trying to find? Step 3 Set up the formula. Step 4 Plug-in the numbers. Solve.**Consider the problem…**“How much force is needed to accelerate a 1400 kg car 2 m/s2? ” Step 1 Read the problem. Draw a picture. 1400 kgcar 2 m/s2 Formula Plug-in Answer F = m = a = Units, units, units!**“How much force is needed to accelerate a 1400 kg car 2**m/s2? ” Step 2 Write down what you know. What are you trying to find? 1400 kgcar How much force? 2 m/s2 Formula Plug-in Answer ? F = 1400 kg m = 2 m/s2 a = Units, units, units!**“How much force is needed to accelerate a 1400 kg car 2**m/s2? ” Step 3 Set up the formula. F = m x a Formula Plug-in Answer ? F = 1400 kg m = m x a 2 m/s2 a =**“How much force is needed to accelerate a 1400 kg car 2**m/s2? ” Step 4 Plug-in the numbers. Solve. 2800 kg x m/s2 or N for newtons…it’s easier to write! Formula Plug-in Answer ? F = 1400 kg m = F = ma 2800 kg x m/s2 1400 kg x 2 m/s2 2 m/s2 a = Units, units, units!**HELPFUL HINTS:**a = F / m F = m x a m = F / a F A M**There are 2 kinds of forces**1) Normal force: the force a surface exerts on an object that is pressing on it**There are 2 kinds of forces**2) Net force: the sum of two or more forces on an object**Let’s see how Newton’s Second Law of Motion applies to**the NFL https://www.youtube.com/watch?v=qu_P4lbmV_I 3:52**Newton’s Third Law: Action Forces = Reaction Forces**For every action there is an equal and opposite reaction. Look at the picture below: What is the action? What is the reaction? As the gases push downward out of the rocket, The rocket is pushed upward by gases.**Let’s see how Newton’s Third Law of Motion applies to**the NFL https://www.youtube.com/watch?v=e1lzB36aHD4 4:13**Newton's 3 Laws Review**An object will remain at rest unless acted upon by an “unbalanced” force. An object in motion will continue with constant speed and direction, unless acted on by an unbalanced force. 1 This law shows how force, mass and acceleration are related as shown in the equation below: Force = mass x acceleration 2 For every action there is an equal and opposite reaction. 3**The Story of Newton’s Apple**Newton sat under an apple tree, and an apple fell on his head. That falling apple gave him a revelation and led him to describe a force called GRAVITY. But DON’T think of gravity as falling… It is the pull(force) that an object has on another object.**Gravity is the force that ALL objects in the UNIVERSE exert**between each other... Newton said that gravitational force depends on 2 things: The DISTANCE of the objects The MASS of the objects More Fg Less gravitational force compared to... Less Fg The blue objects have more gravitational force between them than the green objects. This is because the blue objects have more MASS. more gravitational force here