1. Thursday, September 3 Word of the Day –Newton’s second law of motion: acceleration is equal to the force divided by the mass of the object Warm-Up:A horizontal force of 100 N pushes a box across a floor at a constant speed –What is the net force acting on the box? –What is the force of friction on the box? Phil Physicer weighs 600 Newtons and stands on 2 bathroom scales. One scale reads twice as much as the other, what are the scale readings?

2. Monday, May 4 Word: –Terminal speed: the max speed a person in free fall reaches where there is no more acceleration Warm-Up: –What is the difference between velocity and acceleration? –The moon has 1/6 the gravity of earth. If an object has a mass of 120 kg. What is its mass on the moon?

3. Tuesday, May 5 Word: –Newton’s Third Law: to every action there is an equal and opposite reaction Warm-Up: –A wedge of cheese has a mass of 0.6 kg. What is its weight in Newtons? –A girl pulls a 10-kg wagon with 30 N of force. What is the acceleration on the cart?

4. Chapter 3 Newton’s Second Law of Motion – Force and Acceleration

5. Acceleration Bubble Gum Physics Lab What is acceleration, how would you define it? How did the bubble gum lab show acceleration?

6. Galileo’s Definition Change in Velocity can be any of 3 things: –Change in speed –Change in direction –Change in both speed and direction A car has 3 things that change the velocity. What are they? –Gas –Brake –Steering Wheel

7. Examples 1.Suppose you are driving 30 miles per hour, then in the next second you are up to 35 miles per hour, and the next second 40 miles per hour. What is your acceleration? a.5 miles per hour per second 2.Now you slow down and go from 40 miles per hour to 35 to 30 each second. What is the acceleration? What is this type of acceleration often called? a.-5 mph/sec b.deceleration

8. An object falling without air resistance is in free fall. The force acting to accelerate the object is gravity. The acceleration on all objects is 9.8 (10) m/s 2. Draw a picture of an object being dropped from the side of the building. Draw where you think the object will be at 1s, 2s, and 3s.

9. Acceleration and Force Acceleration is directly proportional to net force –Greater Force = Greater Acceleration –If you push a shopping cart it accelerates. If you apply four times the net force, how much greater will the acceleration be? 4 times greater

10. Mass vs. Weight Circle which object you would rather kick: –A soccer ball or a bowling ball –A tin can or a can full of rocks –A pillow or a wall –A piece of paper or a piece of wood

11. Explain Can you scientifically explain why you would rather kick the lighter object? –More massive objects have more inertia –What does that mean? –They want to move less so kicking them will hurt more!

12. Mass vs. Weight Not the same thing Mass = amount of matter in an object; measure of inertia Weight = force due to gravity that acts on a mass Actually 9.8 N, but for this class we will round to 10

13. Mass vs. Weight Practice If you weigh 100 kg, how many Newtons do you weigh? –1000 N If a bag of potatoes weights 100 N, how many kg is the bag? –10 kg

14. Newton’s Second Law of Motion Links force, acceleration, and mass The law states: –The acceleration produced by a net force on an object is directly proportional to the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object. What does this mean? –Acceleration is produced by force and increases as net force increases –The object accelerates in the same direction as the force –Acceleration decreases as the mass of an object increases

15. Calculation Practice Practice: Fill in the blanks 1.A 5-kg bag of sand has a weight of 50 N. When dropped its acceleration is 1.a = 50N / 5kg = 10 m/s 2 2.A 10 kg bag of sand has a weight of 100 N. When dropped its acceleration is 1.a = 100N / 10kg = 10 m/s 2 3.Calculate the free-fall acceleration of a 20 kg bag of sand. 1.a= 200N / 20kg = 10 m/s 2 a = F/m Acceleration = Force divided by mass

16. Calculating Acceleration You should have noticed a common theme on the last slide… –Acceleration due to gravity is a set amount 10 m/s 2 –If we drop an object and it has been falling for 4 seconds, what is the speed?

17. Which parachute will drop faster? Why? –Air Resistance/Drag lessens the acceleration –Terminal speed is reached when there is no more acceleration (95- 125 miles per hour for a human skydiver) –Terminal Velocity – direction and speed when there is no acceleration