Newton’s Laws of Motion and Rocketry

1. Newton’s Laws of Motionand Rocketry

2. Newton’s Laws of Motion • The Laws of Motion are governed by three principles developed by one man by the age of 24! Who is that man? • Sir Isaac Newton (1643-1727), a jack of all trades: physicist, mathematician, astronomer, alchemist and philosopher.

3. Newton’s Laws of Motion will help us answer the following questions and many more • Why aren’t you falling out of your seats? • Why is it so hard to push a car out of the mud? • Why is it even harder to push a cruise ship off the dock? • Why is it harder to pick up a boulder than a basket ball? • Why is it harder to walk on ice than on the pavement? • All of these questions can be answered by Newton’s Three Laws of Motion. Together, the three laws will help us describe how rocketry works; our first unit of the year.

4. Newton’s 1st Law (a.k.a.)Law of Inertia • Task #1: Yank a piece of paper out from under a text book & then from under a notebook. • Respond in Your Notebook: • Why did you put the paper & book in the orientation you did? • Was there a difference between the textbook & the notebook? Explain. • What did you have to do the fail at the trick? (Describe what you did differently to make the trick fail.)

5. Law of Inertia • Every object in motion stays in motion and any object at rest stays at rest until acted upon by an outside force. • Inertia: is the term for the property of matter that resists change in its state of motion. • Why aren’t you falling out of your seats? • Why is it so hard to push a car out of the mud? • Why is it even harder to push a cruise ship off the dock? • Objects at rest want to stay that way!

6. What would happen if a pitcher threw a baseball in space? Why? Objects in motion want to stay that way! Why is it harder to stop an 18-wheeler moving at 60 mph than a compact car moving at the same speed? • If no breaks were applied, would the two vehicles move forever? Why or Why not? • Which would most likely stop first? • But I thoughtobjects in motion wanted to stay that way??? • Friction is a force opposing motion, caused by the contact of two surfaces.

7. Drawing Net forces

8. 1 • The law of inertia is most commonly experienced when riding in cars and trucks. • Consider the unfortunate collision of a car with a wall. • Upon contact with the wall, an unbalanced force acts upon the car to abruptly decelerate it to rest. • Any passengers in the car will also be decelerated to rest if they are strapped to the car by seat belts. • Being strapped tightly to the car, the passengers share the same state of motion as the car. • As the car accelerates, the passengers accelerate • As the car decelerates, the passengers decelerate As the car maintains a constant speed, the passengers maintain a constant speed.

9. But what would happen if the passengers were not wearing the seat belt? What motion would the passengers undergo if they failed to use their seat belts and the car were brought to a sudden and abrupt halt by a collision with a wall? 1

10. 1 • If the car were to abruptly stop and the seat belts were not being worn, then the passengers in motion would continue in motion. • Assuming a negligible amount of friction between the passengers and the seats, the passengers would likely be propelled from the car and be hurled into the air. • Once they leave the car, the passengers become projectiles and continue in projectile-like motion. 1) From: The Car and The Wall http://www.geocities.com/Athens/Academy/9208/cci.html

11. There are many more applications of Newton's first law of motion2. Several applications are listed below - it is hoped that you could provide explanations for each application. • blood rushes from your head to your feet while quickly stopping when riding on a descending elevator. • the head of a hammer can be tightened onto the wooden handle by banging the bottom of the handle against a hard surface. • a brick is painlessly broken over the hand of a gullible father by slamming it with a hammer. (CAUTION: do not attempt this at home!) • to dislodge ketchup from the bottom of a ketchup bottle, it is often turned upside down and, thrusted downward at high speeds and then abruptly halted. • headrests are placed in cars to prevent whiplash injuries during rear-end collisions. while riding a skateboard (or wagon or bicycle), you fly forward off the board when hitting a curb or rock or other object which abruptly halts the motion of the skateboard. 2) From: Lesson 1: Newton's First Law of Motion http://www.geocities.com/Athens/Academy/9208/u2la.html#first

12. Newton’s 1st Law (a.k.a.) Law of Inertia • Task 2: Pull the Paper out of a book standing on one end. Change the force of the pull several times. • Respond in Your Notebook: • Did the book’s inertia change by standing it on one end? • Did the book’s inertia change with the force of the pull? • What factors influence this task? How could you test each factor?

13. Law of Inertia An object’s orientation can change it’s inertia by altering its center of gravity! Center of Gravity: the average location of the weight of an object.

14. Lab Stations: More, Plop, Oops! You will be working in groups to complete three lab stations. At each station, you will find the lab procedure, materials needed to complete each lab and a set of questions about the lab to be answered. • You will be given a limited time at each station. In this time, the experiment is to be conducted, cleaned up and the questions are to be answered. • Leave the station exactly as you found it! • Hand in questions.

15. While all objects exhibit the property of inertia, all objects do not have the same inertia! Think about it… is it easier to kick an empty can or a full can? Inertia is affected by mass. Mass: is the quantity of matter in an object. **Mass is not weight!** Weight: is a measure of an object’s gravitational attraction to earth. Weight can change. Mass does not! Why is it easier to kick an empty can than a full can? The full can had more mass and therefore, more inertia. In other words, the more mass an object has, the more it will resist change in its state of motion.

16. How does this apply to rocketry? • Our model rockets must have engines that exhibit enough force to change their inertia if we want to get then off the ground. The bigger the rocket, the bigger that force must be!

17. Newton’s 2nd Law • Task 1: Drop a textbook from shoulder height, then drop a piece of paper from shoulder height. • Respond in Your Notebook: • What happened to the two falling objects? • How can you explain your observations in number 1? • What caused the two objects to fall? Was anything working against the falling objects? How can you tell?

18. Newton’s 2nd Law • Task 2: Place the piece of paper on top of the textbook and drop the two objects from shoulder height. Then place the piece of paper underneath the textbook and drop the two objects from shoulder height. • Respond in Your Notebook: • What happened to the book and piece of paper each time? • How can you explain what happened to the piece of paper in the two different scenarios? • If air resistance was not a factor, do you think these two objects would fall at the same time?

19. Newton’s 2nd Law (a.k.a.) F = m x a • The acceleration produced by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object. • So what does this mean??? The amount of force applied to an object is equal to the mass of the object multiplied by its acceleration due to that force: F = m x a • What is acceleration? • How fast something speeds up.

20. Gravity • Gravity is a force of attraction between two bodies with mass. • Since all object have mass, all objects exert gravity on all other objects. Even you have your own gravity. • So why don’t we observe our own gravity? Because compared to the earth, our mass is very, very small…so small that our own gravity is too small to observe. • More mass = More Gravity

21. Gravity • Gravity is a force applied to all objects by the earth. No matter what the object, the acceleration due to gravity is: 9.8 m/s2

22. Example: A textbook has a mass of 1 kg and a piece of paper has a mass of 0.0001kg. What is the force of gravity on each of these falling objects? F = ma F= ma Ftextbook = 1kg x 9.8 m/s2 Fpaper = 0.0001kg x 9.8m/s2 Ftextbook = 9.8 N Fpaper = 0.00098 N A Newton, N, is equal to a kg m/s2 Was the force of gravity on the textbook and the paper the same? Does this mean that they should fall at the same time or not? What was the real reason that they did not fall at the same time? Air resistance works against the force of gravity. Air Resistance: Friction due to air. Because the piece of paper has more air resistance, its acceleration due to gravity is slowed. Other forces are resisted by friction.

23. Apollo 15’s Dave Scott tried a similar experiment on the moon and dropped a hammer and a feather at the same time. What do you think happened? • http://video.google.com/videoplay?docid=6926891572259784994&q=feather+and+the+moon • Dave Scott showed us what free fall would look like. • Free Fall: falling free of air resistance or other constraints.

24. On earth, we do not have the luxury of experiencing free fall, but we can experience something similar… • Terminal Velocity: • The point in movement where the force propelling the object forward is equal to the forces resisting the forward motion (i.e. air resistance/friction = gravity) causing the speed of the object to be constant.

25. Think about it… If a heavy person and a light person open their parachutes together at the same altitude and each wears the same size parachute, who will reach terminal velocity first? who will reach the ground first?

26. Suppose that air resistance could be eliminated so neither the elephant nor the feather would experience any air drag during the course of their fall. • Which object - the elephant or the feather - will hit the ground first? • Many people are surprised by the fact that in the absence of air resistance, the elephant and the feather strike the ground at the same time. 3) From: Elephant and Feather-Air Resistance http://www.geocities.com/Athens/Academy/9208/efff.html

27. In the absence of air resistance, both the elephant and the feather are in a state of free-fall. That is to say, the only force acting upon the two objects is gravity. • This force of gravity is what causes both the elephant and the feather to accelerate downwards. The force of gravity experienced by an object is dependent upon the mass of that object. • The elephant has more mass than the feather. Due to its greater mass, the elephant also experiences a greater force of gravity. • That is the Earth is pulling downwards upon the elephant with more force than it pulls downward upon the feather. • Since weight is a measure of gravity's pull upon an object, it would also be appropriate to say that the elephant weighs more than the feather.

28. Why then does it hit the ground at the same time as the feather?3 • When figuring the acceleration of object, there are two factors to consider - force and mass. • The elephant experiences a much greater force (which tends to produce large accelerations. Yet, the mass of an object resists acceleration. • The greater mass of the elephant (which tends to produce small accelerations) offsets the influence of the greater force It is the force/mass ratio which determines the acceleration.. Even though a baby elephant may experience 100,000 times the force of a feather, it has 100,000 times the mass…the force/mass ratio is the same for each.

29. The greater mass of the elephant requires the greater force just to maintain the same acceleration as the feather. • We say that mass and acceleration are inversely proportional. A large mass will accelerate slowly, while a small mass will accelerate quickly with the same force.

30. Other forces are affected by the area the force is applied to. How does a snow shoe work? • Because your mass and the acceleration due to gravity do not change, the force you apply to the ground is the same with each step. • So why then can you walk across deep snow without sinking in a snow shoe and not in a regular boot? • The snow shoe allows the force of your step to be applied over a large surface area. • The force per unit area is a called pressure.

31. Can you survive a skydiving accident if your chute does not open? • Ask Peggy Hill or Mr. Mal

32. Practice Problems • Your Assignment: Complete the following problems in your notebook using complete sentences. • Pg. 71-73, # 3, 7, 8, 9, 11, 12, 13, 14, 25, 27, 30, 33

33. Inertia, Gravity and Satellites4 • Satellites require great speeds to avoid crashing! • Altitude determines it speed • a satellite in low orbit (about 800km/497mi) from the Earth is exposed to an immense amount of gravity • has to move at considerable speed to keep from crashing • Gravity is important to keep the satellite from moving off into space. 4) From: Satellite Orbits http://www.eduspace.esa.int/subtopic/default.asp?document=297

34. As the satellites are in orbit outside the atmosphere there is no air resistance, and therefore, the speed of the satellite is constant. • If orbiting inside the atmosphere, the satellite must overcome air resistance (must be able to speed up when it slows down because of air resistance)4. • Satellites are both natural (the moon) and man made.

35. F.Y.I. on Satellites Polar Orbits • have an inclination near 90 degrees. • the satellite sees virtually every part of the Earth as the Earth rotates underneath it. • It takes approximately 90 minutes for the satellite to complete one orbit. • These satellites have many uses such as measuring ozone concentrations in the stratosphere or measuring temperatures in the atmosphere. 5) From: Types of Orbits http://marine.rutgers.edu/mrs/education/class/paul/orbits2.html

36. Sun Synchronous Orbits5 • These orbits allows a satellite to pass over a section of the Earth at the same time of day. • These orbits are used for satellites that need a constant amount of sunlight. • Satellites that take pictures of the Earth would work best with bright sunlight, while satellites that measure long wave radiation would work best in complete darkness.

37. Geosynchronous Orbits/Geostationary Orbits5 • circle the Earth at the same rate as the Earth spins. • allow the satellite to observe almost a full hemisphere of the Earth. • These satellites are used to study large scale phenomenon such as hurricanes, or cyclones. These orbits are also used for communication satellites. • Telecommunication needs to "see" their satellite all time and hence it must remain stationary in the same positions relative to the Earth's surface • The disadvantage of this type of orbit is that since these satellites are very far away, they have poor resolution. The other disadvantage is that these satellites have trouble monitoring activities near the poles.

38. Newton’s 3rd Law • Slap your desk. • Slap it again, a little harder this time. • What do you notice? • If you remember Newton’s Second Law where F = m x a, then you remember that if F is constant, than the smaller “m” will feel a greater “a.” • Unfortunately for you, the desk did not move as much as your hand in this one.

39. Newton’s 3rd Law • Did you know that it is impossible to hit a piece of paper with a huge amount of force? Try it! • Why? All forces require equal and opposite forces. Remember, F = ma. The paper does not have enough mass to hit you back with the same amount of force.

40. Newton’s 3rd Law • These are examples of Newton’s Third Law; action forces always equal reaction forces. • Whenever one object exerts a force on a second object, the second object exerts an equal but opposite force on the first object. • Newton’s Third Law says that for every action there is an equal but opposite reaction.

41. 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.

42. Rifle has Ma Bullet is Shot Out by force from gun powder Bullet has mA • Have you ever shot a rifle and felt the kickback? Where does that come from and how does this help us explain how a rifle works? • The rifle shoots the bullet with a force and the bullet pushes the rifle back with the same force. Because the rifle has a much larger mass than the bullet, it will accelerate much less than the bullet.

43. So what does this mean for Rocketry? • People used to believe that rockets pushed against the atmosphere. But, if that were true, they would not be able to change the acceleration once they got into space…we know that isn’t true. • Rocket pushes burning fuel out the back and the burning fuel pushes the rocket back. exhaust rocket

44. What about two forces in opposite directions? Me You • I hit a football and you hit a football in the opposite direction. • The two opposite forces “cancel” each other out and the ball goes nowhere. • The football will give us both a reaction force though.

45. Why do geese fly in a “V”? (pg. 76) • The wings of a bird push air downwards. In turn, the air reacts by pushing the bird upwards. • Create an updraft in the air around them. • The updraft is off to the side and behind the flapping (or front) bird. • The updraft is used by the bird behind for additional lift making flying easier.

46. Practice Problems • Complete the following problems in your notebook: Pg. 83-85, #6-8, 16, 17, 22, 23, 25, 29, 35, 36

47. So…going back to our first questions: • Why aren’t you falling out of your seats? • Why is it so hard to push a car out of the mud? • Why is it even harder to push a cruise ship off the dock? • Why is it harder to pick up a bolder than a basket ball? • Why is it harder to walk on ice than on the pavement?