Earth’s ForcesChapter 14

Lesson 1: Forces and Motion

DEMO

Watch your teacher perform the Egg Drop demonstration.

Predict: What will happen to the egg if a force caused the pan to suddenly move?

Think about this: What forces are acting on the objects

before, during, and after the demonstration.

What happened to the egg and why do you think this was the outcome?

Forces and Motion

A force is a push or pull; things move when they are acted on by a force.

Often, more than one force acts on an object at the same time. The total of all the force on the object is called the net force. When forces act against each other with equal

strength in opposite directions, the net force is ZERO and the object will not move.

When one force is greater than the other the net force is NOT ZERO and the object will move.

Net Forces (aka Vector Forces)

F = 20 NEast

F = 20 NWest

F = 18 NEast

F = 20 NWest

Forces and Motion

In science, any change in an object’s motion is called acceleration.

Refers to an object’s Increasing speed Decreasing speed Changing direction Changing speed and direction

Newton’s Three Laws of Motion

Sir Isaac Newton was an English scientist in the late 1600’s who proposed three laws of motion.

Newton’s three laws of motion explain how inertia, an object’s mass, acceleration, and the forces acting on the object are related.

1st Law of Motion

Objects at rest will remain at rest unless acted on by a nonzero net force.

Objects moving at a constant speed and direction (velocity) will continue moving at that rate unless a nonzero acts on it.

The tendency of an object to resist a change in motion is called inertia.

http://teachertech.rice.edu/Participants/louviere/Newton/law1.html

Question

If you kick a soccer ball, and no one stops it, why does it eventually slow and stop? Friction and gravity are forces that act against it

How can I make the soccer ball go further? Reduce the friction (on concrete or ice vs grass)

or increase the force that you kick with (kick it harder)

If I roll a soccer ball and a bowling ball with the same force on the street, which one would be harder to stop? The bowling ball because it has more mass and

it’s inertia is greater

DEMO

Think about what happens to the pipes when you drop the cup. What causes this to occur?

Try This: Put the penny on your elbow then try to catch the penny with the same hand. How is this possible? Can you explained this using Newton’s 1st Law of Motion?

2nd Law of Motion

An object’s acceleration depends on its mass (the amount of matter in an object) and the net force acting on it.

The mathematical equation for this law is: Force (F) = Mass (M) x Acceleration (A)

Or: Acceleration (A) = Force (F) / Mass (M)

http://teachertech.rice.edu/Participants/louviere/Newton/law2.html

Question

On a swing, who would require more force to push? Why? Jonathan Vilma: or Steve

Urkel6’11” / 230 lbs 5’6” / 110

lbs

Question

On a swing, if you applied the same force to each person, who would have the greatest acceleration? Why? Jonathan Vilma: or Steve

Urkel 6’11” / 230 lbs 5’6” / 110

lbs

DEMO

Using your left pinky finger, try to push the paperback book across the table.

Using the same finger, try to push the hardback book across the table.

Which required more force? Why? Can you explain this using Newton’s

2nd Law of Motion?

3rd Law of Motion

If one object exerts a force on another object, then the second objects exerts a force of equal strength in the opposite direction.

“For every action there is an equal and opposite reaction.”

http://teachertech.rice.edu/Participants/louviere/Newton/law3.html

Question

What happens when you blow up a balloon, then let it go (without tying then open end)?

Why does this happen (using Newton’s 3rd Law of Motion)?

DEMO

Watch what happens when you drop the basketball and tennis balls separately.

Watch what happens when you drop the basketball and tennis balls together.

What’s the difference between the two drops?

Why do you think this happened? Explain this using Newton’s 3rd Law of Motion.

Lesson 2: Gravity and Motion

Newton’s Three Laws of Motion

DEMO

Make a fork and spoon magically “levitate” on the glass using the provided materials.

Think about this: Which of Newton’s Laws are you using to complete this “magic trick”?

Gravity and Motion

The force that pulls an apple to the ground also pulls satellites (including the moon and International Space Station) toward Earth, keeping them in orbit.

Gravity attracts all objects toward one another.

Newton’s Law of Universal Gravitation states that every object in the universe attracts every other object.

Gravity and Motion

The strength of the force of gravity between two objects depends on two factors: The mass of the objects The distance between the objects

Gravity, Mass, and Weight

Mass is the amount of matter in an object Earth is extremely massive and

therefore exerts more force than you The force of gravity decreases as the

distance increases The further an object, the less gravity is

exerted on the object

Gravity, Mass, and Weight

Gravity, Mass, and Weight The measure of the force of gravity on an

object is called weight.

If you go to the moon, what would change, your mass or your weight? Your WEIGHT would change depending on your

location (like the moon) because the gravity is different there (1/6th as much)

Why is gravity different on the moon than on Earth? The moon has less mass than Earth, so it also

has less gravitational pull.

Objects in Orbit

Recall Newton’s 3 Laws of Motion and think about which one may explain this: What keeps objects orbiting Earth (like

the moon, satellites, or the International Space Station)?

Newton concluded that inertia (1st Law of Motion) and gravity keep Erath in orbit around the sun, and the moon and ISS in orbit around Earth.

Orbital Motion of the Moon

Spaced Out Sports

Spaced Out Sports (SOS)

You will be working on a group project creating a game that can be played on the International Space Station.

To do this, you will be putting to use the information we learned about forces, Newton’s Laws of Motion, and gravity.

Think About It:

How are things different in space than they are here?

How do objects move differently in space?

If I hit an object in space, with micro-gravity, what would happen to that object?

SOS Video: Newton’s Laws in Space

SOS Video: Sports in Space