Physics Talk 2.3Newton’s Second Law

Do NowDoes 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: 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, 2011Do 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:

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 minutes6-7 10 minutes

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

DO NowExplain the relationship between Mass,

Acceleration, and Force.Hint: keep mass constant, explain what happens to

force and accelerationHint: keep force constant, explain what happens to

mass and accelerationHint: given a constant acceleration, how are mass

and force related?

Vocab: Mass, Acceleration, Force, increase, decrease, constant

November 9, 2011HW: 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 NowLO/SCPhysics TalkPTG

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. 162Explain why force is measure in Newtons

which is defined as1N=1kg*m/s2

Physics Talk 2.3What is Newton’s

Second Law?Relationship between

force, mass, and acceleration

F=ma

Physics Talk 2.3What is the equation

for Newton’s Second Law?

What does each variable represent?

amF

a = acceleration (m/s2)F = force (Newton – N)m = mass (kg)

Physics Talk 2.3What 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 2.3What 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 1A 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 kga = 430m/s2

Unknown: ForceTool: F = maSolution:

F = 0.058kg*430m/s2

F = 24.95 kg*m/s2

F ≈ 25N

Sample Problem 1Could an identical

force accelerate a 5.0 kg bowling ball at the same rate?

Given:F=25Nm = 5.0kg

Unknown: acceleration

Tool: F=maSolution:

25N=5kg*a m/s2

25N/5kg = a

Sample Problem 1Could 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.

asm

akg

smkg

2

2

/5

5

/25

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

25N/5kg = a

Sample Problem 2A 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=4Nm=275g = 0.275 kg

Unknown: acceleration

Tool: F=maSolution:

4N=0.275kg*a m/s2

asm

akg

smkg

2

2

/5.14

275.0

/4

Gravity, Mass, Weight, and Newton’s Second LawWhat 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 LawHow do you

calculate an object’s weight?

What do the variables mean?

gmw

amF gravitygravity

w = weightm = mass in kgg = 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 solveA 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 ForcesWhat 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 DiagramExample of free

body diagram for

Free-Body DiagramExample 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