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# Newton's Laws & Gravitation

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• Remember that Force is also a vector - it has to include direction in the answer.
• If I send a ball rolling across the floor, it will continue at the same speed and direction unless it encounters another force. What forces might it encounter
• If I send a ball rolling across the floor, it will continue at the same speed and direction unless it encounters another force. What forces might it encounter
• If I send a ball rolling across the floor, it will continue at the same speed and direction unless it encounters another force. What forces might it encounter
• ### Newton's Laws & Gravitation

1. 1. Newton's Laws & Gravitation
2. 2. Newton's Second Law <ul><li>Newton's Second Law: When an object is acted on by an unbalanced force, it will accelerate (speed up, slow down or change direction) in the direction of that force. </li></ul><ul><ul><li>In other words, if you push on an object, the amount that it accelerates depends on two things: </li></ul></ul><ul><ul><ul><li>the mass of the object (bigger mass = more inertia) </li></ul></ul></ul><ul><ul><ul><li>the magnitude of the force with which you push </li></ul></ul></ul><ul><li>Force = Mass x Acceleration (F=ma) </li></ul>
3. 3. F=ma <ul><li>Force = Mass x Acceleration </li></ul><ul><li>Force = 10 kg x 10 m/s 2 </li></ul><ul><li>100 kg • m/s 2 = 100 Newtons </li></ul><ul><li>Force = 100 N to the right </li></ul>100 N 10 kg 10 m/s 2
4. 4. <ul><li>Force = Mass x Acceleration </li></ul><ul><li>100 N = 100 kg x ? m/s 2 </li></ul><ul><li>? N = 100 kg x 10 m/s 2 </li></ul>1 m/s 2 1000 N 100 kg ? m/s 2 100 N 100 kg 10 m/s 2 ? N
5. 5. <ul><li>Force = Mass x Acceleration (F=ma) </li></ul><ul><li> Force = 1,000 kg x .05 m/s 2 </li></ul><ul><li> Force = 50 kg • m/s 2 </li></ul><ul><li>(kg • m/s 2 = Newtons) </li></ul><ul><li> Force = 50 N East </li></ul>Calculating Force East
6. 6. Practice Problem <ul><li>Force = Mass x Acceleration (F=ma) </li></ul><ul><li>Find the net force. </li></ul><ul><li>Plug in the #'s for force and acceleration. </li></ul><ul><li>Solve for acceleration. </li></ul>Answer: A 3 kg • m/s 2  100kg = 0.03 m/s 2 to the left
7. 7. Newton's Third Law <ul><li>Newton's Third Law : for every action there is an equal and opposite reaction. </li></ul><ul><ul><li>&quot;action&quot; & &quot;reaction&quot; are the result of forces </li></ul></ul><ul><ul><li>the forces don't act on same object </li></ul></ul><ul><ul><ul><li>the &quot;action&quot; is on one object (i.e. woman pushes cart) </li></ul></ul></ul><ul><ul><ul><li>the &quot;reaction&quot; is on another (i.e. cart exerts force on woman) </li></ul></ul></ul>
8. 8. GRAVITY <ul><li>Gravity is a pull (force) between any two objects that have mass, such as the earth and an object on its surface. </li></ul><ul><li>The gravitational force between two masses is directly proportional to the mass of each object. </li></ul><ul><ul><li>The more &quot;stuff&quot; you've got (mass), the more gravitational attraction there is. </li></ul></ul><ul><li>The gravitational force between two masses is inversely proportional to the distance between those two objects. </li></ul><ul><ul><ul><ul><li>The more space between your &quot;stuff&quot; and mine, the less gravitational attraction there is. </li></ul></ul></ul></ul>
9. 9. LAW OF UNIVERSAL GRAVITATION <ul><li>Two things affect gravity: </li></ul><ul><ul><li>Mass of objects </li></ul></ul><ul><ul><li>Distance between objects </li></ul></ul><ul><li>G = 6.672x10 -11 </li></ul><ul><li>(Universal Gravitational Constant) </li></ul><ul><li>F g measured in Newtons (N) </li></ul>
10. 10. Projectile Motion <ul><li>What do Newton's Laws of Motion say about this cannon? </li></ul><ul><ul><li>The cannon & ball will not move unless acted on by an unbalance force (explosion within the cannon) </li></ul></ul><ul><ul><li>The ball will accelerate proportionately to the amount of force (the bigger the &quot;bang&quot; inside the cannon, the faster the ball accelerates. </li></ul></ul>Newton's Cannon <ul><ul><li>The cannon will &quot;kick&quot; back in response to an equal and opposite force exerted from the ball exploding forward. </li></ul></ul><ul><ul><li>The pull of gravity results in centripetal acceleration, where the ball continually &quot;falls&quot; around the earth in orbit. </li></ul></ul>
11. 11. Free Fall <ul><li>When the only force acting on a falling object is gravity, it is said to be in free fall . </li></ul><ul><li>As an object falls, it picks up speed. </li></ul><ul><ul><li>Gravity causes the rate at which it falls to increase (accelerates, speeds up). </li></ul></ul><ul><li>All objects fall at the same rate. </li></ul><ul><ul><li>Earth produces the same acceleration on an object, no matter what it's mass is: 9.8 m/s 2 toward the ground . </li></ul></ul><ul><ul><li>In reality, some objects fall slower due to air resistance </li></ul></ul><ul><ul><li>Without air resistance (in a vacuum), all objects fall at an identical speed </li></ul></ul>
12. 12. Acceleration Due to Gravity <ul><li>Both objects accelerate at the same rate. </li></ul><ul><li>Both objects will reach the ground at the same time. </li></ul>
13. 13. Terminal Velocity <ul><li>When the forces of gravity and air resistance equal out, an object reaches terminal velocity . </li></ul><ul><ul><li>This means the falling object will no longer accelerate (it won't get any faster) </li></ul></ul>skydiver illustration <ul><li>When the skydiver opens a parachute, it dramatically increases air resistance. </li></ul><ul><ul><li>This counters the force of gravity and slows the skydiver down. </li></ul></ul>
14. 14. Weight vs. Mass <ul><li>Mass = how much &quot;stuff&quot; a thing has </li></ul><ul><ul><li>...the amount of matter in an object </li></ul></ul><ul><ul><li>Measured with a balance </li></ul></ul><ul><ul><li>Stays the same regardless of gravity </li></ul></ul><ul><li>Weight = gravity's pull on that &quot;stuff&quot; </li></ul><ul><ul><li>Weight = mass x acceleration due to gravity </li></ul></ul><ul><ul><li>Measured with a spring or digital scale </li></ul></ul><ul><ul><li>Weight is a force, measured in Newtons </li></ul></ul><ul><li>W = m • g </li></ul>
15. 15. Calculating the Force of Weight <ul><li>Weight = m x g </li></ul><ul><li>m (mass) has to be in kg </li></ul><ul><li>g (acceleration due to gravity) = 9.8 m/s 2 </li></ul>For a 150 lb person: W = 68 kg x 9.8 m/s 2 W = 666 Newtons