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Solve for the Unknown in the following diagram:

Learn to solve unknowns in physics diagrams involving mass, weight, and gravity. Understanding Newton's laws and forces. 8

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Solve for the Unknown in the following diagram:

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  1. Solve for the Unknown in the following diagram: • 60 m/s2 right • 60 m/s2 left • 10 m/s2 left • 4 m/s2 right

  2. Solve for the Unknown in the following diagram: • 20 kg • 12 kg • 5 kg • 4 kg

  3. Solve for the Unknown in the following diagram: • 60 N • 50 N • 20 N • 120 N

  4. Solve for the Unknown in the following diagram: • 400 N • 300 N • 200 N • 60 N

  5. Free-Falling Mr. Rodgers—Mexican Cliffs--1990 Bodies

  6. Gravity • Force that is exerted between all objects. • All matter has gravity!! • Gravity is the force that pulls you toward the center of the Earth. • Weight is a measure of the force of gravity on an objects mass. We can use Newton’s 2nd law to convert between mass and weight!

  7. Converting between Mass and Weight • Because gravity is a force, it causes things to accelerate at a constant rate!! • The acceleration due to gravity(g) has a numerical value of 9.8 m/s2. • Using Newton’s 2nd Law, we can substitute “g” for “a” and get:

  8. Where: = Force of gravity(Weight) in Newtons(N) = mass in kilograms(kg) = acceleration due to gravity(9.80 m/s2)

  9. m = 85 kg Fg = ?

  10. Fg = 4500 N m = ?

  11. A block has a mass of 2.5 kg. What is the weight of the block? • 24.5 N • 12.5 N • 3.92 N • .255 N

  12. A child’s new bicycle weighs 290 N. Find the mass of the bicycle. • 35.8 kg • 29.6 kg • 23.4 kg • 17.3 kg

  13. Let’s get back to things falling!!!

  14. When things do fall, do they continue to accelerate(get faster) until they hit the ground? Why?

  15. Free-Falling Objects(cont.) • We know friction opposes the motion of objects “on the ground”! • Are there any forces that oppose the motion of a “free-falling object”??? Thank goodness for Air Resistance!!!

  16. Air Resistance • Force that opposes the motion of a free-falling object! • Terminal Velocity—Highest velocity reached by a falling object. Why?? • As objects fall, they get faster, but also the amount of air resistance gets greater. • Eventually, the force down and the force up are equal. Then what?

  17. Now look at the forces! Pay attention to what happens as the guy falls? Now look at the accelerations!

  18. Terminal Velocity • Terminal velocity happens because the force of gravity pulling down and the force of air resistance pushing up are the same size. • According to Newton’s 1st Law, with balanced forces, “there will be no change in the motion!!” • Object will not speed up, slow down, or change direction!

  19. Newton’s 3rd Law Revisited: • How do rockets get launched into space? • What does that have to do with Newton’s 3rd Law?

  20. Momentum • Momentum is the product of an objects mass and velocity!! • It is the strength of an objects motion!! p = m v Where: p = momentum m = mass v = velocity

  21. What does momentum have to do with Newton’s 3rd Law(and Rockets)? • Conservation of Momentum—Total momentum of a system of objects remains constant unless acted on by some unbalanced force. • Rocket—Gases go one way, rocket moves the other way. • Momentum of the gases one way, must EQUAL the momentum of the rocket the other way!!

  22. Conservation of Momentum

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