6. Seat Belts In your lab book, start a new page. Title it “Newton’s First Law of Motion and Seat Belts” Be sure to make an entry in your table of contents as well.
7. Seat Belts Suppose you had to design a seat belt for a race car that can go 300 km/h (about 200 mi/h). How would it be different from one available on passenger automobiles? Make a heading in your lab book that will title your thoughts and take five minutes to jot down ideas for a safe race car seat belt.
8. Seat Belts Share your ideas with your table partner. If you think of other ideas, be sure to add them to your lab book. Now turn to your group of four and share your ideas – make any additions or changes to your ideas.
10. Seat Belts Turn in your textbook to page 266. Read the Investigate carefully so that you understand how you will conduct this lab. Remember: each place in the text book that has a pencil symbol is a place where you must write in your lab notebook!
11. Seat Belts Newton’s First Law An object at rest stays at rest an object in motion stays in motion in a straight line with constant speed unless acted upon by a net, external force. Review!
12. Law of Inertia An object at rest stays at rest… Think about the lab you just participated in and write an example of an object staying at rest in your notes. “The part of the law of inertia that says an object at rest stays at rest is shown by…”
13. Law of Inertia “…an object in motion continues at the same speed in a straight line…” Think about the lab you just participated in and write an example of an object staying at rest in your notes. “The part of the law of inertia that says that an object in motion continues at the same speed in a straight line…” BE CAREFUL! Gravity is an external force acting on an object rolling down an incline!
14. Law of Inertia “…unless acted upon by a net, external force.” Think about the lab you just participated in and write an example of a net external force. “The part of the law of inertia that says a net, external force will change the motion of an object at rest OR an object in motion is shown by…”
15. 3 collisions in every accident In every car accident, there are three collisions. when the car strikes an object – such as another car, a tree, a light-pole as the car stops, the bodies in the vehicle continue to move until they collide with the structure of the car (seatbelt, steering column, air bags, windshield) the body stops, but the internal organs keep moving until the body wall exerts a force on them and brings them to rest Take Notes!
16. 3 collisions in every accident While safety features such as seat belts and air bags have dramatically reduced fatalities in automobile accidents, it is still possible to suffer serious or fatal consequences in a car crash because of the third collision.
17. 3 collisions in every accident In one recorded accident, a single vehicle with only the driver inside failed to follow a turn and struck a telephone pole. The seat belt and air bag prevented any serious injuries apart from a few bruises, but the driver died. The autopsy showed that the driver’s aorta (the largest blood vessel in the body – it leads out of the heart to the body) tore in the collision of the heart with the ribs and the man bled to dead internally.
18. What makes a seat belt safe? In the second part of the lab, you investigated the effect of different types of seat belts. Keep in mind that the stopping force of each type of seatbelt was the same because you released the cart from the same height each time. Yet, some seat belts did more damage to the clay drivers than others. Why?
19. Pressure In the thin wire seat belt, all of the stopping force was concentrated onto a small area. With a broader strip of material, that same stopping force was spread out over a larger area of contact. Force that is spread out over a given area is called pressure. Take Notes!
21. Pressure In the picture, the pressure exerted by the feet of the boy on the right is greater than the pressure exerted by the feet by the boy on the left. In our lab, the pressure of the wire as a seat belt was greater than the pressure exerted by the ribbon. It is the pressure, not force, that determines how much damage a seat belt does to the body. Take Notes!
22. Pressure Formula Pressure = Force/area where… force is in Newtons area is in square meters (m2) and pressure is in N/m2 which is also called a pascal. Take Notes!
23. Sample Problem Sample Problem Two students have the same mass and apply a constant force on the ground of 450 N while standing in the snow. Student X is wearing snowshoes that have a base area of 2.0 m2. Student Y, without snow shoes, has a base area of 0.1 m2. Why does Student Y sink into the snow? Take Notes!
24. Sample Problems What is the pressure exerted when a force of 10 N is applied to an object with the following areas? 1.0 m2 0.2 m2 15 m2 Take Notes!
25. A video There is a famous demonstration of pressure using a bed of nails. Here is one version
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