1. Free body diagrams, acceleration, quiz Friday, November 6, 2015

2. Friday, 11/6 Unit 4: Forces  Respond to the following questions for both pictures. 1. Using your knowledge of inertia, describe how the image demonstrates Newton’s 1 st Law of motion. 2. What could you do to change the motion of the bus or the race car? Upcoming dates  Friday, 11/6 – quiz  Monday, 11/16 – quiz  Monday, 11/16 – review due at when the late bell rings  Wednesday, 11/ 18 – Unit 4 test  W/O 11/23 – Thanksgiving break  Friday, 12/11 – 2NW extra credit due

3. Weight vs. Mass  Mass is matter (atoms)  Weight is the force of gravity acting on mass.  Weight is represented by the symbol F g  F g will always act on an object.

4. How to Calculate force of gravity (weight) Note: when calculating F g acceleration will always be 9.8 m/s 2

5. Example – calculating weight (F g ) A child pulls a wagon with a mass of 6 kg, ten meters across the grass to the garage. The child applies a 10 N force to overcome 2Ns of friction. Calculate the weight of the wagon. G: m = 6kgE: F g = (m)(a)S: 58.8 N U: F g S: F g = (6)(9.8)

6. Practice calculating weight (F g )

7. 245 N 14.7 N 1127 N

8. How to calculate force Note: acceleration will not Be 9.8 m/s 2 unless the object Is in free-fall.

9. How to Calculate net force

10. Net Force - answers

11. Newton’s 2 nd Law – Practice problem 1 A car has a mass of 550 kg. 1. Find the weight of the car on Earth 2. Find the net force needed to accelerate the car at 12 m/s 2. 3. If a net force of 2200 N were to act on the car, what would its acceleration be?

12. Newton’s 2 nd Law – Practice problem 2 A sled weighs 2500 N on Earth 1. What is the mass of the sled? 2. What is the mass of the sled on the moon, where g = 1.6 m/s 2 ? 3. What is the weight of the sled on the moon? 4. What net force is needed to accelerate the object at 4.0 m/s 2 on the moon?

13. Free body diagram (FBD)  Pictorial representation of forces acting on an object.

14. Free body diagram steps 1. Replace the object with a dot. 2. Identify the force pairs acting on the object 3. Identify contact forces acting on the object. Remember that only something that is physically touching the object can apply a contact force Possible types of contact forces – push, tension, normal, and friction 4. Add arrows force and label the forces 5. Add any force values that are known

15. Example - FBD A child pulls a wagon with a mass of 6 kg, ten meters across the grass to the garage. The child applies a 10 N force to overcome 2Ns of friction. Calculate the weight of the wagon.