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### Physics Talk 2.3

Newton’s Second Law

September 30, 2013HW:

- Do Now:
- Copy LO and SC
- 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

Notebook Set up

- Read Investigate pg. 157-159
- Set up Notebook for tomorrow

September 28, 2010HW: Grade Report Signed, Missing work due Friday

- Do Now:
- 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:

- #1-5 30 minutes
- 6-7 10 minutes

Exit Ticket (on a half sheet of paper)

- 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

September 29, 2010HW: 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 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

- Could an identical force accelerate a 5.0 kg bowling ball at the same rate?

- Given:
- F=25N
- m = 5.0kg
- Unknown: acceleration
- Tool: F=ma
- Solution:
- 25N=5kg*a m/s2
- 25N/5kg = a

Sample Problem 1

- Could an identical force accelerate a 5.0 kg bowling ball at the same rate?

- No, an identical force would not accelerate the bowling ball at the same rate.

- Solution:
- 25N=5kg*a m/s2
- 25N/5kg = a

Sample Problem 2

- 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?

- Given:
- F=4N
- m=275g = 0.275 kg
- Unknown: acceleration
- Tool: F=ma
- Solution:
- 4N=0.275kg*a m/s2

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)

September 30, 2010HW: 2.3 PTG #1-4, 6, 7, 9-11, Due Friday

- 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

Balanced and Unbalanced Forces

- What is a free-body diagram?
- When will an object accelerate?

- A diagram showing the forces acting on an object
- Balanced force=no acceleration
- Unbalanced forces=acceleration

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

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