Force and Motion Unit

Force Unit

FORCE

There is sound with this slide.1Force Unit

Unbalanced Forces

Forces Day 1 ObjectivesI will knowthe nature of forces and their interactions with matter.I will be able todescribe and solve for balanced and unbalanced forces.

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How do forces affect the motion of an object?

A force can cause a resting object to move, or it can accelerate a moving object by changing the objects speed or direction.

Can you give some examples of when you could apply a force?

What Is a Force?A force is a push or a pull that acts on an object.

4Pull a wagon, push a crate, turn a doorknob, One newton(N) is the force that causes a 1-kilogram mass to accelerate at a rate of 1 meter per second each second (1 m/s2). 1 N =1 kgm/s2What is the unit for force?

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When the forces on an object are balanced, the net force is zero, and there is no change in the objects motion.

Combining ForcesWhen an unbalanced force acts on an object, the object accelerates.

How do forces affect the motion of an object?

6There is sound with this slide.The net force is the overall force acting on an object after all the forces are combined.NET ForcesForces in the same direction add together.Can you think of an example of two forces in the same direction, that would make a bigger force?

7Get books out ahead of time. You can change the type of book to whatever you have available in your room.

Examples: TWO people pushing a large crate. TWO football players pushing on the blocking sleds.Lets do a little activity! 1. Everyone take your physical science book and stand up. 2. Lets pretend you will gently push the book forward along the floor with a force of 10 N. 3. Stop. 4. Now push the book along the floor a little harder with another forward force of 20 N. 5. Return to your seat.6. What was your net force?

10 N + 20 N = 30 NMy NET FORCE WAS 30 N!

What would happen if forces would occur in opposite directions?Forces in the opposite direction subtractfrom one another.

9Get books out ahead of time. You can change the type of book to whatever you have available in your room.Lets do another little activity! 1. Everyone take your physical science book and stand up. 2. Lets pretend you will gently push the book along the floor forward with a force of 20 N. 3. Stop. 4. Now push the book along the floor in the opposite direction with a little harder with a force of 30 N. 5. Return to your seat.6. What was your net force?20 N - 30 N = -10 NMy NET FORCE WAS -10 N!

The two groups pull with equal forces in opposite directions. The forces combine to make a net force of zero. An example of combining forces:

11Forces can add together or subtract from one another.Combining Forces

Adding forcesSubtracting forces12Point out the size difference of the adding forces compared to the size of the subtracting forces.Forces can add together or subtract from one another.Combining Forces

Adding forcesSubtracting forcesEqual and opposite forces13Point out situation A, where two are added together and make a bigger one.Point out situation B, where they are in opposite directions, then equal a smaller arrow pointing left.Point out situation C, where they are equal but opposite (this will be like Newtons Third Law of Motion).Small Group PracticeWhat is the net force of the following:60 N east, 80 N west45 N north, 20 N north25 N to the right, 55 N to the left90 N south, 90 N north35 N south, 15 N north5 N to the left, 9 N to the left3 N to the left, 3 N to the rightNext to your answer, write if it is balanced or unbalanced.

Make sure they understand that they will be finding the net force AND telling if it is balanced or unbalanced.

14Group Practice -- answersWhat is the net force of the following:60 N east, 80 N west = 20 N west; unbalanced45 N north, 20 N north = 65 N north; unbalanced25 N to the right, 55 N to the left = 30 N left; unbalanced90 N south, 90 N north = 0 N; balanced35 N south, 15 N north = 20 N south; unbalanced5 N to the left, 9 N to the left = 14 N left; unbalanced3 N to the left, 3 N to the right = 0 N; balancedNext to your answer, write if it is balanced or unbalanced.

Make sure they understand that they will be finding the net force AND telling if it is balanced or unbalanced.15

In what direction does Earths gravity act?

GravityEarths gravity acts downward toward the center of Earth.

16EXAMPLE: Earth exerts an attractive, downward force on a boulder. The supporting rock exerts an upward force on the boulder. The forces are balanced.

How do gravity and air resistance affect a falling object?Gravity causes objects to accelerate downward, whereas air resistance acts in the direction opposite to the motion.17Falling ObjectsBoth gravity and air resistance affect the motion of a falling object.As objects fall to the ground, they accelerate and gain speed. Terminal velocity is the constant velocity of a falling object when the force of air resistance equals the force of gravity.

This flying squirrel takes advantage of air resistance to slow its fall and increase the distance covered in the jump.Example:

18Summary Think, Pair & ShareCan you think of other examples of forces?Baseball hitting a ballFoot kicking a soccer ballCar hitting another car in an accidentFingers pushing a key on a keyboard

Accept any reasonable answer. The above are possible answers.19Summary Day 1

Using complete sentences, explain the forces involved with this picture. Also, how would you describe the net force?

Students can put the answers to this in their notebook , or use this as an exit question.20Summary Day 1 -- answer

Earth exerts an attractive, downward force on this boulder. The supporting rock exerts an upward force on the boulder. The forces are balanced.

End of What is Force Notes pagePut this on back of what is force pagesNewtons Law of Universal Gravitation:Every mass attracts every other mass with a force directly proportional to the masses and inversely proportional to the distance between them.

Does the suns force have more effect on Earth or the dwarf planet Pluto?Earth (closer)

Force Unit

Newtons 1st& 3rd Laws of Motion

We will cover the 2nd Law tomorrow.25Objectives Take notes Cornell Style in your Notebooks over this section I will understand Newtons first and third Laws of Motion.I will be able to describe examples of Newtons first and third Laws of Motion.I will be able to review the Inverse Square Law.

Newtons 1st Law of Motion

1st Law: An object in motion will stay in motion,

an object at rest will stay at rest,

unless acted on by an outside force.

What outside force is slowing the ball to a stop?FRICTIONVOCABULARY:Inertia: the tendency of an object to resist any change in its motion.

Inertia is a NeSA-Science term.31Mass is a quantitative measure of inertia.

Which boxer has more inertia?

The bigger one!

WHY?

MORE MASS!

Turn to a partner Which dog has more inertia?

THE BIGGER ONE!more mass more inertia!

Newtons Third Law of Motion

3rd Law: For every action there is an equal but opposite reaction!

NESA ---Science Vocabulary = all forces occur in equal and opposite pairs.38One force is called the ACTION FORCE.The other force is called the REACTION FORCE.a. It does not matter which is called action or reaction.b. They are a pair in a single interaction.

c. They are EQUAL in strength

d. They are opposite in direction.Can you give examples of Newtons 3rd Law?

A tug of war. A rocket being launched. You pushing on a table.40rocket

fuel

Examples:

If you have TWO DIFFERENT masses.a. They will have equal forces.b. Their velocities will be different.

Cannonballs velocity is greater

Example of different velocitiesCannons velocity is smallerThis is due to the 2nd LawA small mass = a greater acceleration A larger mass = a smaller acceleration

Push down on your lab table.Turn to a partner

Discuss what each of you think the lab table does to your hand.

Table pushes back!

They are EQUAL but OPPOSITE reactions!

Table pushes back!

If you have unequal Forces then you have acceleration NOT the 3rd Law.

Bottom of Cornell NotesUsing complete sentences describe two examples of the 1st law that you see occur in your life and describe two examples of the 3rd law that you see occur in your life.