Day 3 – Free body diagrams

1. Day 3 – Free body diagrams Mr. Lambert Integrated Science 1A Trimester 1, 2014

2. Bell Ringer Many video games follow some physics laws just like the real world. One good example of this is Mario Bros. • When Mario jumps into a “?” block, it drops a mushroom. • Draw a Free Body Diagram (FBD) of the block. Include the force of Mario’s head and the force of gravity that pulls the block back down. • If the block accelerates upward, are the forces on it balanced or unbalanced? How do you know?

3. Agenda • Bell Ringer • Review Lab simulations • Balloon lab • Exit Slip

4. Learning Targets On your Bell Ringer Sheet, write the following: We will explain how unbalanced forces effect acceleration

5. Units Mass = kilograms (kg) or grams (g) Velocity (Speed) = Acceleration = Force = Newtons (N)

6. What forces are acting on the box? Are these forces balanced or unbalanced? What is the net force? Is the box accelerating?

7. Are these forces balanced or unbalanced? What is the net force? Is the box accelerating?

8. Look at the forces acting on the box. Which is greater? Are the forces balanced? What is the net force?

9. Are the forces balanced? Which direction is the net force? Therefore, what is happening to the box?

10. Are the forces balanced? What is the net force?

11. Net force?

12. Key points • Object only accelerates if there is a net force! • If there is zero net force, the object is moving at a constant velocity (this includes zero velocity!)

13. On a half-sheet of paper answer the questions A group of engineers is doing research on how to maximize the efficiency of hybrid cars. They decide to do some test runs first. • Draw a free body diagram of the hybrid car before it begins to move. • Draw a free body diagram of the hybrid car as it begins to accelerate. Compare and contrast the forces in the free body diagrams above. How do the differences in the forces from the first FBD to the second FBD explain the change in motion of the hybrid car?

14. Question continued…. The engineers decide to modify some components of the hybrid car. • On hybrid car A, the engineers made the car bigger and used a stronger, heavier metal. Using Newton’s Second Law, explain why hybrid car A will have a slower acceleration. • On hybrid car B, the engineers added a more powerful engine, increasing the force of the car. Using Newton’s Second Law, explain why hybrid car B will have a faster acceleration.

15. The first FBD shows only gravitational force pushing down and normal force pushing up. Both of these forces are the same and therefore cancel out. There are no forces pushing it along the road. Since there is no net force, and since the forces are balanced, the car does not move and does not accelerate. • The second FBD shows an engine force (thrust) that moves the car. There is also frictional force pushing in the opposite direction. Since the car is accelerating, the engine force is bigger than the frictional force. The forces are therefore unbalanced and there is a net force, causing the car to accelerate.

16. 1. The bigger car and heavier metal increase the mass of the car. Since newton’s second law states the F = ma, if the mass of the car increases, and the force stays the same, the acceleration has to decrease. 2. The more powerful engine will increase the force that moves the car. Since Newton’s Second Law states that F = ma, if the force on the car increases, and the mass stays the same, the acceleration has to increase.

17. Balloon Rocket lab • We will investigate and prove Newton’s Second Law

18. Balloon Rocket Lab • Materials: • 6 washers • 1 straw • 1 index card • 3 balloons (YOU ONLY GET 3, SO DO NOT POP THEM) • 2 paper clips • Tape (will be floating around room)

19. Safety • Always aim your rocket TOWARD the wall. • Make sure paper clips are well attached • Materials manager should be responsible for inflating balloons (don’t swap, there are germs)

20. Making your rocket • Tape index card to straw. • Push paper clip hooks through index card. • Inflate your balloon to a medium size. • Tape the balloon to the side of the index card.

21. Follow directions in the handout! • Fill it out as you work. • Model lab

22. Predictions In your lab notebooks, predict: • What will happen to the acceleration of your balloon when you add mass to it? When we add mass to the balloon . . . • What will happen to the acceleration of your balloon when you add a second balloon? When we add a second balloon . . .

23. Follow-up Questions • How will the acceleration of the rocket be affected if you replace the fishing line with yarn? What will happen to the unbalanced force acting on the rocket? • If you tilt the fishing line upward, you are changing the unbalanced force. How are you affecting the unbalanced force, and what is the effect on the acceleration of the rocket?

24. Net force Problems

25. Net force Problems • Jaquan is sumo wrestling Jaqari. Jaquan pushes with a force of 25 N, and Jaqari pushes with a force of 20 N. What is the net force? Which direction will they accelerate? • Jen is skydiving. As she free falls, gravity pulls her down with a force of 1000 N. Air resistance pushes up with a force of 800 N. What is the net force? Which direction does she accelerate?

26. Written Assessment

27. Exit Slip When Mario jumps on a goomba (his mortal enemies), the goomba is squished beneath him. • Draw a free body diagram of the goomba. • Label the 100 Newton force of gravity pulling Mario down and the 10 Newton force of the goomba’s head trying to push back on him. • Subtract the forces. Is it balanced or unbalanced? Which way does the goomba accelerate? • Which direction is the net force on the goomba?