Newton’s Second Law of MotionMrs. Anna WardJames Martin MS

Draw the following in your science notebook…

FORCE = MASS times ACCELERATIONFORCE = 1000 x .05FORCE = 50 NEWTONS 

Do Now!!!

F=ma

Test on Newton’s Laws on Friday Notebook Check next Friday

Announcements

Individual Mini Labs at our desk on Newton’s Second Law

Guided Notes on Newton’s Second Law (F=ma)

Partner Mini-Lab on Newton’s Third Law Guided Notes on Newton’s Third Law

Video on Newton’s Laws

Agenda

1. Directions: Tie a paper clip to each end of the yarn.

2. Hold the single paper clip in the middle of your desk; hang the other end of the yarn over the edge. Let go and observe.

3. Add one more paper clip to the hanging end and repeat the experiment. Observe what happens.

4. Repeat step #3.

How are force and acceleration related?

Questions:1. What happened each time that

you let go of the yarn?2. Explain the relationship between

the number of hanging paper clips and the motion of the paper clip on the table.

Questions for your notebook:

Newton’s Second Law states that the acceleration of an object increases with increased force and decreases with with increased mass.

Newton’s Second Law

Force, mass, and acceleration have a relationship

http://www.d123.org/olhms/ebarlos/documents/PSC02BAD.pdf

In simple terms…

We describe this relationship using the formula:

F=maor

Force=mass x acceleration

Newton’s 2nd law

Force is measured as mass with acceleration, so…

Kg/m/s2

Which is also known as a NEWTON

1 Kg/m/s2 = 1 Newton or 1 N

Newton’s Second Law

What force is needed to accelerate a 10 kg shopping cart 3 m/s2?

What do you know? What do you want to find out? Write the formula: Substitute into the formula: Calculate & Simplify: Check that your units agree Answer: F=30 N

Newton’s 2nd Law—Apply the Knowledge

What force is needed to accelerate a 20 kg boulder to 2 m/s2?

What do you know? What do you want to find out? Write the formula: Substitute into the formula: Calculate & Simplify: Check that your units agree Answer: F=40 N

CFU

If a force of 35N is added to a box and it accelerates to a rate of 7 m/s2, what is the mass of the box?

What do you know? What do you want to find out? Write the formula: Substitute into the formula: Calculate & Simplify: Check that your units agree Answer: mass=5 kg

CFU

1. What net force is required to accelerate a car at a rate of 2 m/s2 if the car has a mass of 3,000 kg?

2. A 10 kg bowling ball would require what force to accelerate down an alleyway at a rate of 3 m/s2?

3. Victor has a car that accelerates at 5 m/s2. If the car has a mass of 1000 kg, how much force does the car produce?

Independent Practice F=ma

1. With a partner, hook the two spring scales together.

2. Pull gently on your spring scale while your partner holds but does not pull on the other side.

3. Observe and record the amount of force that is shown on your scale and on your partner’s scale.

4. Both of you pull together. Observe the forces shown on each side.

Newton’s Third Law: Investigation

1.What happened to your partner’s force as your force increased?

2.What happened when you both pulled?

3.Explain why you think what you observed in each case happened.

4.Can you think of a way to use the scales to show Newton’s first or second law?

Investigation Questions:

Newton’s Third Law states that every time one object exerts a force on another object, the second object exerts a force that is equal in size and opposite in direction back on the first object.

Newton’s Third Law

Sometimes referred to as law of “EQUAL and OPPOSITE”

For every reaction, there is an “equal and opposite” reaction

What ever happens, there is an exact (but opposite) force that happens as well.

Newton’s Third Law—in more simple terms

So if Nixon pushes against a wall with a force of 25N, how much force does the wall exert on him, and in what direction?

CFU…

The force that is exerted on an object and the force that exerts back are known as action-reaction pairs.

Example: When Abed bangs his toe into the leg of the table, the same amount of force he exerts on the table is exerted back on his toe.

Action-Reaction Pairs

http://www.d123.org/olhms/dedie/documents/2-3Forces.pdf

Action-Reaction Pairs

What are some other examples of Action/Reaction Pairs?

Brainstorm…

What are the action reaction pairs with:

Jumping? Walking? Catching a Ball? Larkam’s bat hitting a baseball? The door shutting? Asia’s book bag hitting the floor?

CFUs

http://www.youtube.com/watch?v=2OJjbztWitk

Video…

Suppose Robert is holding a basketball while standing still on a skateboard. Justin and the skateboard have a mass of 50kg. He throws the basketball with a force of 10N. What is his acceleration before and after he throws the ball?

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