# Earth’s Forces - PowerPoint PPT Presentation

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Chapter 14. Earth’s Forces. 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:

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Earth’s Forces

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Chapter 14

## Earth’s Forces

### 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?

• 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.

F = 20 N

East

F = 20 N

West

F = 18 N

East

F = 20 N

West

### 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 Urkel

6’11” / 230 lbs5’6” / 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 lbs5’6” / 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.

### DEMO

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

### 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

• 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.

### 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.