Physics Talk 2.3 Newton’s Second Law

Do Now Does an object have acceleration if it is traveling at constant speed? Why or why not? Use definitions and equations to support your answer.

November 9, 2011 Do Now: Agenda: Learning Objective: Success Criteria: WDYS/WDYT pg. 157 Agenda: Do Now LO and SC Investigate Physics Talk, Notes Active Physics Plus Learning Objective: Students use F=ma to solve problems relating to Newton’s Second Law of Motion Success Criteria: Identify the forces acting on an object Determine when the forces on an object are either balanced or unbalanced Compare amounts of acceleration semi-quantitatively Apply Newton’s Second Law of Motion Apply the definition of the Newton as a unit of force

Read Investigate pg. 157-159

November 9, 2011 Do Now: Agenda: Learning Objective: Success Criteria: Read Investigate pg. 157-159 Agenda: Do Now LO and SC Investigate Physics Talk, Notes Active Physics Plus Learning Objective: Students use F=ma to solve problems relating to Newton’s Second Law of Motion Success Criteria: Identify the forces acting on an object Determine when the forces on an object are either balanced or unbalanced Compare amounts of acceleration semi-quantitatively Apply Newton’s Second Law of Motion Apply the definition of the Newton as a unit of force

Investigate: List all materials in your investigate 5 minutes Set up your notebook by turning the questions into statements in your notebooks so you can just fill in the blanks when doing your lab, do #’s 1-3 first… 20 minutes #1-5 30 minutes 6-7 10 minutes

DO NOW: For your lab..Copy this table and finish any set up of your notebook. Force Mass Acceleration

DO Now Explain the relationship between Mass, Acceleration, and Force. Hint: keep mass constant, explain what happens to force and acceleration Hint: keep force constant, explain what happens to mass and acceleration Hint: given a constant acceleration, how are mass and force related? Vocab: Mass, Acceleration, Force, increase, decrease, constant

November 9, 2011 HW: PTG 1-4, 6, 7, 9-11 Do Now: How did the mass on the car change the force needed to push it? Agenda: Do Now LO/SC Physics Talk PTG L.O. Students use F=ma to solve problems relating to Newton’s Second Law of Motion S.C. Identify the forces acting on an object. Determine when the forces on an object are either balanced or unbalanced. Compare amounts of acceleration semi-quantitatively. Apply Newton’s Second Law of Motion. Apply the definition of the Newton as a unit of force

In your notebook: Look at pg. 162 Explain why force is measure in Newtons which is defined as 1N=1kg*m/s2

Physics Talk 2.3 What is Newton’s Second Law? Relationship between force, mass, and acceleration F=ma

Physics Talk 2.3 a = acceleration (m/s2) F = force (Newton – N) What is the equation for Newton’s Second Law? What does each variable represent? a = acceleration (m/s2) F = force (Newton – N) m = mass (kg)

Physics Talk 2.3 What is a Newton? What causes acceleration? The Newton is the unit for force. 1 N is the force required to make on kg of mass accelerate at 1m/s2 1N = 1 kg*m/s2 Unbalanced forces

Physics Talk 2.3 What are some examples of Newton’s second law? Does Newton’s 2nd Law ever stop working? If you push a small cart with a large force, it will accelerate a great deal. If you use the same force on a car, it will accelerate less. No, there is always acceleration, it just may be too small to measure.

Sample Problem 1 A tennis ball with mass 58g accelerates at 430m/s2 when it is served. What is the force responsible for this acceleration? Given: m =58 g = 0.058 kg a = 430m/s2 Unknown: Force Tool: F = ma Solution: F = 0.058kg*430m/s2 F = 24.95 kg*m/s2 F ≈ 25N

Sample Problem 1 Given: F=25N m = 5.0kg Unknown: acceleration Tool: F=ma Solution: 25N=5kg*a m/s2 25N/5kg = a Could an identical force accelerate a 5.0 kg bowling ball at the same rate?

Sample Problem 1 Could an identical force accelerate a 5.0 kg bowling ball at the same rate? Solution: 25N=5kg*a m/s2 25N/5kg = a No, an identical force would not accelerate the bowling ball at the same rate.

Sample Problem 2 Given: F=4N m=275g = 0.275 kg Unknown: acceleration Tool: F=ma Solution: 4N=0.275kg*a m/s2 A tennis racket hit a sand-filled tennis ball with a force of 4 N. While the 275 g ball is in contact with the racket, what is its acceleration?

Gravity, Mass, Weight, and Newton’s Second Law What is the acceleration due to gravity? What does this mean about the force of gravity? What is weight? 9.8 m/s2 If you drop a 1kg mass, there is a force of 9.8N acting on the object The vertical, downward force exerted on a mass as a result of gravity

Gravity, Mass, Weight, and Newton’s Second Law How do you calculate an object’s weight? What do the variables mean? w = weight m = mass in kg g = acceleration due to gravity (9.8 m/s2)

Do Now: Use the concept of F=ma to explain why someone has different weights on different planets. Agenda: Do Now LO/SC Physics Talk Vector Addition Learning Objectives: Students use F=ma to solve problems relating to Newton’s Second Law of Motion Explain the difference between mass and weight Success Criteria: Identify the forces acting on an object Determine when the forces on an object are either balanced or unbalanced Compare amounts of acceleration semi-quantitatively Apply Newton’s Second Law of Motion Apply the definition of the Newton as a unit of force Describe weight as the force due to gravity on an object

Do Now-Use Gutau to solve A football with mass 84g accelerates at 370m/s2 when it is thrown. What is the force responsible for this acceleration? A person has a mass on earth of 60Kg and decides to take a trip to the moon where gravity is a rate of 2m/s2 What is the person’s weight on the moon?

Balanced and Unbalanced Forces A diagram showing the forces acting on an object Balanced force=no acceleration Unbalanced forces=acceleration What is a free-body diagram? When will an object accelerate?

Free-Body Diagram Example of free body diagram for

Free-Body Diagram Example of a free-body diagram for a car moving on the road at a constant velocity. Is the car accelerating? Since the car is traveling at a constant speed, it is not accelerating. This means that the force of the road on the tires is equal to the air resistance and we have balanced forces.

What do you think now? In your notebook: Pg. 170