1. Warm Up 10/21/15 A man hits a golf ball (0.2 kg) which accelerates at a rate of 20 m/s2. What amount of force acted on the ball? You push a friend sitting on a swing. She has a mass of 50 kg and accelerates at a of 4 m/s2. Find the force you exerted. How does mass effect the momentum of an object? (will a large or small object be harder to stop and why?) Two cars of equal masses but different velocities. Which car has the greater momentum, the car with the higher velocity or the car with the lower velocity? What is the momentum of an object that is not moving?

2. Momentum

3. All moving objects have what Newton called a “quantity of motion.” What is this quantity of motion? Today we call it momentum. Momentum is a characteristic of a moving object that is related to the mass and the velocity of the object.

4. Momentum = Mass x Velocity Mass is measured in kilograms and velocity is measured in meters per second Unit for momentum is kilogram-meters per second (kg x m/s). Like velocity, acceleration, and force, momentum is described by its direction as well as its quantity.

5. Equation p = momentum (kg*m/s) + direction m = mass (kg) v = velocity (m/s) + direction p = m * v Momentum is a vector quantity

6. The momentum of an object is in the same direction as its velocity. The more momentum a moving object has, the harder it is to stop. The mass of an object affects the amount of momentum the object has. For example, you can catch a baseball moving at 20 m/s, but you cannot stop a car moving at the same speed. The car has more momentum because it has a greater mass.

7. The velocity of an object also affects the amount of momentum an object has. For example, an arrow shot from a bow has a large momentum because, although it has a small mass, it travels at a high velocity.

8. Figure 17 Momentum An object’s momentum depends on velocity and mass. Problem Solving If both dogs have the same velocity, which one has the greater momentum?

9. Sample Momentum Problems Which has more momentum: a 3.0 kg sledgehammer swung at 1.5m/s, or a 4.0 kg sledgehammer swung at 0.9 m/s? Read and Understand –What information are you given? Mass of smaller sledgehammer = Velocity of smaller sledgehammer = Mass of larger sledgehammer = Velocity of larger sledgehammer =

10. Look Back and Check –Does your answer make sense? The 3.0 kg hammer has more momentum than the 4.0 kg one. This answer makes sense because it is swung at a greater velocity.

11. Practice Momentum Problems 1.A golf ball travels at 16 m/s while a baseball moves at 7 m/s. The mass of the golf ball is 0.045 kg and the mass of the baseball is 0.14 kg. Which has a greater momentum? 2. What is the momentum of a bird with a mass of 0.018 kg flying at 15 m/s?

12. Conservation of Momentum The word conservation has a more specific meaning in physical science. In physical science, conservation refers to the conditions before and after some event. An amount that is conserved is the same amount after an event as it was before. The total amount of momentum objects have is conserved when they collide.

13. Momentum may be transferred from one object to another, but none is lost. This fact is called the law of conservation of momentum. The law of conservation of momentum states that, in the absence of outside forces, the total momentum of objects that interact does not change.

14. The amount of momentum is the same before and after they interact. The total momentum of any group of objects remains the same, or is conserved, unless outside forces act on the objects. Friction is an example of an outside force.

15. Collisions With Two Moving Objects In Figure 18A, a train car travels at 4 m/s down the same track as another train car traveling at only 2 m/s. The two train cars have equal masses. The blue car catches up with the green car and bumps into it. During the collision, the speed of each car changes.

16. The blue car slows down to 2 m/s, and the green car speeds up to 4 m/s. Momentum is conserved – the momentum of one train car decreases while the momentum of the other increases.

17. Collisions With One Moving Object In Figure 18B, the blue car travels at 4 m/s but the green car is not moving. Eventually, the blue car hits the green car. After the collision, the blue car is no longer moving, but the green car travels at 4 m/s. Even though the situation has changed, momentum is conserved. All of the momentum has been transferred from the blue car to the green car.

18. Collisions With Connected Objects Suppose that, instead of bouncing off each other, the two train cars couple together when they hit. Is momentum still conserved in Figure 18C? After the collision, the coupled train cars make one object with twice the mass.

19. The velocity of the coupled trains is 2 m/s – half the initial velocity of the blue car. Since the mass is doubled and the velocity is divided in half, the total momentum remains the same.

20. Save Your Egg!!! The purpose of the “Egg Drop Project” is to design an apparatus, using the physics concept of momentum and impulse, which will keep an egg safe when dropped out of a window. groups of 2-3 students will design an apparatus with materials you bring to class Thursday The apparatuses will be dropped on Monday during class from the 2 nd floor. Those whose eggs do not break will win the competition!

21. Egg Drop of Doom In class project The device holding the egg must contain at least four (4) different materials. Just wrapping the egg in bubble wrap will not be accepted. The size has limitations – fit on sheet of paper External attachments like a parachute, or hot air balloon may not be used. The egg must be easily inserted and removed from the device within two (2) minutes.

22. At the event, the egg participants will be given a raw Large Grade A egg that has been weighed and labeled. Students will load the egg, without the assistance of adults. Students are responsible for the egg during loading, dropping and unloading. After the egg is loaded, the device will be weighed. The weight of the egg, which could vary between eggs, will be subtracted from the weight of the package.

23. Egg Drop of Doom The device will be dropped free fall at a height of 2 story building. There will be only one drop. The team must unload and hand the egg to the judge once the drop is complete within two minutes.

24. Scoring Winners will be determined by the lightest device that successfully protected the egg. Eggs that do not break or show cracks will be ranked first. A = Egg safely in tack after drop B = Slight crack by no signs of egg leaking out C = Annihilation

25. Using Elastics to allow the egg to have more time to stop by “stretching” out… This doesn’t allow the egg to stop more slowly by “stretching”. MAYBE it acts as a cushion, but definitely not enough cushion for this fall! This is more like it! Attaching elastics so that they will “stretch out” when the apparatus hits the ground!

26. Space and Strength! Give it enough space and make it strong enough.

27. Be sure to take your GOOD idea and make it GREAT! Good idea … a good frame, but work on protection! Choose a good frame so the engineering is visible!

28. Plickers Time Test how much you remember