2. Gravity <ul><li>Gravity is a force of attraction that acts between bodies that have a mass. </li></ul><ul><li>Gravity was discovered by Sir Isaac Newton. </li></ul><ul><li>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. </li></ul><ul><li>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 . </li></ul><ul><li>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. </li></ul>
3. How to Measure Gravity <ul><li>Weight is a measure of how much Earth’s gravity pulls down on an object. </li></ul><ul><li>Mass is the amount of matter in an object, and mass does not change from place to place. </li></ul><ul><li>While your weight would change on the moon, your mass would not change. </li></ul><ul><li>Mass is measured with a balance. </li></ul><ul><li>Weight is measured with a scale. </li></ul><ul><li>Mass and weight are two different things, so we have to use two different units for them. </li></ul><ul><li>Mass is measured in g or kg. Weight is measured in Newtons (N). </li></ul><ul><li>A 10g weighs 1N on Earth. So if a rock had a mass of 30g, it would weigh 3N. </li></ul>
4. Speed <ul><li>Speed is the measure of how far you move in a given time. To find speed you need to know time and distance. </li></ul><ul><li>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. </li></ul><ul><li>The speed of the ball throughout the trip changed. It started off slow and got faster as it rolled down. </li></ul><ul><li>So, this calculation gives you an average speed and describes the movement for the entire trip down the street. </li></ul>
5. Stopping <ul><li>Gravity speeds you up as you go down a hill, but what makes you stop. Friction. </li></ul><ul><li>Friction is the push or pull that opposes motion between two surfaces that are touching each other </li></ul><ul><li>If you are roller blading, you might use the rubber stopper to cause friction against the street to help you stop. </li></ul><ul><li>H.W. Pg. 274, ques. 1 & 2. Page 288, 1-10. </li></ul>
6. Newton’s Three Laws of Motion <ul><li>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. </li></ul><ul><li>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. </li></ul><ul><li>In other words, things don’t stop or start by themselves. The reasons things stop is because of friction. </li></ul>
7. Newton’s Second Law <ul><li>This law involves force, mass and acceleration. </li></ul><ul><li>Law #2: Acceleration depends on the mass of an object and the force pushing or pulling the object. </li></ul><ul><li>Force = mass x acceleration, F=mXa </li></ul><ul><li>Acceleration = force/mass, a=F/m </li></ul><ul><li>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. </li></ul>
8. Newton’s Third Law <ul><li>Law #3: For every action there is an equal and opposite reaction. </li></ul><ul><li>If you push on a wall, the wall is pushing back at you at the same rate. </li></ul>