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# 6th Grade Chapter 10- forces and motion

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### Transcript

• 1. Chapter 10 Forces and Motion
• 2. Gravity
• Gravity is a force of attraction that acts between bodies that have a mass.
• Gravity was discovered by Sir Isaac Newton.
• Gravity acts on all objects the same. If you drop a bowling ball and a tennis ball at the same time, they will both hit the ground at the same time because gravity is a constant.
• The more matter something has the more gravitational pull it has. Our moon is much smaller than Earth and only has about 1/6 the amount of gravity .
• Jupiter’s gravity is about 2.5 times stronger than Earth’s because of its size. That is why people weigh different weights on different planets.
• 3. How to Measure Gravity
• Weight is a measure of how much Earth’s gravity pulls down on an object.
• Mass is the amount of matter in an object, and mass does not change from place to place.
• While your weight would change on the moon, your mass would not change.
• Mass is measured with a balance.
• Weight is measured with a scale.
• Mass and weight are two different things, so we have to use two different units for them.
• Mass is measured in g or kg. Weight is measured in Newtons (N).
• A 10g weighs 1N on Earth. So if a rock had a mass of 30g, it would weigh 3N.
• 4. Speed
• Speed is the measure of how far you move in a given time. To find speed you need to know time and distance.
• If you rolled a ball down a hill that was 100 meters long and it took 20 seconds to reach the bottom, its speed is 5 m/s. So the equation for velocity equals, v=d/t or distance over time.
• The speed of the ball throughout the trip changed. It started off slow and got faster as it rolled down.
• So, this calculation gives you an average speed and describes the movement for the entire trip down the street.
• 5. Stopping
• Gravity speeds you up as you go down a hill, but what makes you stop. Friction.
• Friction is the push or pull that opposes motion between two surfaces that are touching each other
• If you are roller blading, you might use the rubber stopper to cause friction against the street to help you stop.
• H.W. Pg. 274, ques. 1 & 2. Page 288, 1-10.
• 6. Newton’s Three Laws of Motion
• Before we talk about the laws, we have to learn about force, which is a push or a pull. Gravity is a force, as well as friction. Everytime you turn a page or open a door, you are using force to do so.
• Law #1: Inertia- An object at rest tends to stay at rest, and a moving object moves in a straight line until it is acted upon by an outside force.
• In other words, things don’t stop or start by themselves. The reasons things stop is because of friction.
• 7. Newton’s Second Law
• This law involves force, mass and acceleration.
• Law #2: Acceleration depends on the mass of an object and the force pushing or pulling the object.
• Force = mass x acceleration, F=mXa
• Acceleration = force/mass, a=F/m
• It takes less force to accelerate something with a small mass. This is why large trucks need more powerful motors to get them going from a complete stop. If you want to go faster, you have to use more force. Like having to pedal harder on a bike.
• 8. Newton’s Third Law
• Law #3: For every action there is an equal and opposite reaction.
• If you push on a wall, the wall is pushing back at you at the same rate.
• 9. Test In One Week!!!!!!!