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Transcript
1 Isaac Newton (1642 – 1727) Newton’s Laws The Father of Force 2 What is a Force? Force can be defined as a push or a pull. Or anything else that has the ability to change motion 3 Force: kilogram x m/sec2 kg x 2 m/s Easier than saying kilogram m/sec2 N Is even easier! 4 To Understand Force… You must understand the difference between AND 2 Kg Mass 5 What is Mass? The amount of “stuff” in an object. 1 Kg Mass 1.5 Kg Mass Mass is measured in Kilograms 2 Kg Mass 6 How is Mass Different Than Weight? Weight is measurement of FORCE. 2.2 pounds 3.3 pounds 9.8 N 14.8 N (1 kg x 9.86 m/s2) (1.5 kg x 9.8 force due to gravity (9.8 m/s2) 1.0 Kg Mass 4.4 pounds 19.7 N (2 kg x 9.86 m/s2) 6m/s2) force due to gravity (9.8 m/s2) force due to gravity (9.8 m/s2) 1.5 Kg Mass 2.0 Kg Mass DON’T USE kilograms (kg) as a measurement for weight (force) USE pounds (lb) or N for force. 77 1 Kg Mass Different Gravity? Mass is the Same:1 kg But the WEIGHT… 2.2 Pounds On the moon 1.0 kg would weigh 0.3 lbs On the sun 1.0 kg would weigh 59.5 lbs On Mars 1.0 kg would weigh 0.8 lbs What’s “Your Weight On Other Worlds?” http://www.exploratorium.edu/ronh/weight/ 8 These laws explain why objects move (or don't move). Let’s look at Newton's three laws of motion... 9 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. This law shows how force, mass and acceleration are related as shown in the equation below: Force = mass x acceleration For every action there is an equal and opposite reaction 10 Newton’s First Law: Balanced Forces An object will maintain a constant state of motion (balanced). This means an object at rest tends to stay at rest and an object in motion tends to stay in motion Forces that are balanced can be: Not in motion Stay at rest: a book on a table IP&C This is known as Inertia Table pushes up on book Gravity pulls down on book In Motion Stay in motion: a bowling ball tossed in space It will go on and on forever 11 Newton’s First Law: Unbalanced Forces An unbalanced force is a force that changes the motion. The book below slides and then stops because resistant force called friction. Friction is force that opposes motion. In space there is no resistance to cause friction, so a bowling ball would stay in motion ...unless another It kind of object got in reminds of the way… a few movies I’ve seen lately... Force of friction stops the book IP&C 12 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! Newton’s Second Law: Force = Mass X Acceleration 13 Force and acceleration are related You are going down the road on your inline skates. Suddenly you look to your right and see a car accelerating faster coming right for YOU! You look for an escape to your left… Oh no! There’s a rock at the edge of neatly manicured lawn. Which will you choose... A massive car accelerating faster? ...or a medium size rock not in motion? Good Choice Force (car) = mass x acceleration is greater than Force (rock) = mass x acceleration You still might get hurt, but would be much worse off choosing the force of the car over the force of the rock. 14 Solving Force Problems Step 1 Read the problem and write down the formula you will use. Step 2 Plug in the information you know into the formula. Step 3 Solve the math. Step 4 Write down the answer with the correct units. 15 Consider the problem… “How much force is needed to accelerate a 1400-kg car 2 m/s2? ” Step 1 1400-kg car Read the problem, draw a picture How much force? 2 m/s2 F= m= a= Formula Plug-in Units, units, units! Answer 16 “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-kg car 2 m/s2 F= m =1400 kg a = 2 m/s2 Formula Plug-in Units, units, units! Answer 17 “How much force is needed to accelerate a 1400-kg car 2 m/s2? ” Step 3 Set up the formula, F=mxa F= m =1400 kg a = 2 m/s2 Formula Plug-in mxa Units, units, units! Answer 18 “How much force is needed to accelerate a 1400-kg car 2 m/s2? ” Step 4 Plug in the numbers Solve 2800kg x m/s2 F= m =1400 kg a = 2 m/s2 Formula mxa Plug-in 1400 kg x 2 m/s2 Units, units, units! Answer 2800 kg x m/s2 19 Be sure to do the problems: • Helpful Hints: a=F/m F=mxa m=F/a 20 The unit for force: 1 kg x 2 m/s = 1 newton or 1N Which one would you rather write for your answer? 2800 N …I thought so. 21 Newton’s Third Law: Action / Reaction For every action there is an equal and opposite reaction Look at the picture below: What is the action? As the gases push downward out of the rocket, What is the reaction? The the rocket is pushed upward by the gases 22 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. This law shows how force, mass and acceleration are related as shown in the equation below: Force = mass x acceleration For every action there is an equal and opposite reaction 23 Newton’s Laws explain how Earthquakes create such devastation Most of the time the Earth’s massive plates push on each to move very slowly. But, sometimes a massive plate exerts a greater amount of force that accelerate another plate. This results in an earthquake. To learn more go to: http://vcourseware5.calstatela.edu/VirtualEarthquake/VQuakeIntro.html 24 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. 25 Newton’s apple was falling because the massive gravitational force of the Earth was pulling the apple towards Earth... 26 Gravity is the force that ALL objects in the UNIVERSE exert on each other... Newton said that gravitational force depends on 2 things: The DISTANCE of the objects The MASS of the objects LESS gravitational force compared to... MORE gravitation force here. The blue object has more gravitational force than the green object because the blue object has more MASS. 27 Newton’s apple fell because the Earth’s pull of gravity.... The itty-bitty pull of apple is too small to pull the Earth, so it is pulled to the Earth... was more massive than the apple’s pull of gravity on the Earth 28 The moon is a satellite too.. The pull of gravity keeps satellites orbiting around the Earth Satellites are sent away and placed in the 29 exact spot where the Earth’s gravity pulls them into a “continuous free fall” or orbit... The Earth is round and the satellite continues to “just miss” entering into the Earth’s atmosphere. The moon does the same thing. 30 Does the moon’s gravitational pull effect the Earth? Yes, the moon’s gravity is large enough to actually pull water out of the ocean from space… Well, not quite that much...just enough to create motion of the tides. 31 Newton is even credited with inventing CALCULUS. Needless to say, Newton was very important in shaping our understanding of science