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Fall Exam Review

Fall Exam Review. Topics include: Accuracy vs. precision Graphs of motion Force Projectiles Gravitation Circular motion Conservation of energy Work and power. Accuracy vs precision. Accuracy requires a target value

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Fall Exam Review

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  1. Fall Exam Review Topics include: Accuracy vs. precision Graphs of motion Force Projectiles Gravitation Circular motion Conservation of energy Work and power

  2. Accuracy vs precision Accuracy requires a target value Precision reflects how small the data spread is. The smaller the spread, the more precise the data.

  3. Accuracy vs precision

  4. Graphs of motion Read the labels on the axis – is the graph a: position vs time velocity vs time acceleration vs time Look at the shape of the graph: horizontal line = constant value straight line with constant slope = changing value curve = changing value

  5. Graphs of motion Represents how the position changes as time passes. The slope = velocity This graph shows constant velocity. position time

  6. Graphs of motion Represents how the velocity changes as time passes. The slope = acceleration This graph shows constant acceleration. velocity time

  7. Try these… velocity position position time time time Increasing slope Increasing velocity accelerating decreasing slope decreasing velocity accelerating Constant negative slope decreasing velocity accelerating

  8. Force Use a sketch or free-body diagram to identify forces and directions acting on objects. Force is a vector, direction matters. Types of forces include: gravity – between 2 masses (earth and another mass is weight) friction – resistance to motion between 2 surfaces tension – string or wire supporting and objet air – friction due to air applied – any force that acts on an object such as a push or pull normal – force of a surface acting upward on an object centripetal – keeps an object moving in a circle or orbit Net force is the sum of all of the forces acting on an object. find total vertical, total horizontal then if needed use pythagorean theorem to find the resultant force.

  9. Balanced/Unbalanced Forces

  10. Force An 8 kg box is being pushed by two workers across a carpeted floor. One worker pushes with 10 N to the right, the other pushes with 7 N of force in the same direction. The carpet provides 5 N of friction. What is the net force? What is the acceleration of the box?

  11. Force and FBD’s Accelerating left – either applied force w/o friction or just friction. No acceleration vertically Accelerating down and to the left Balanced forces horizontally and vertically. Constant velocity. No horizontal forces. Accelerating downward.

  12. Freefall and projectile motion • Object is in the air • Free fall has no horizontal velocity ( just dropping) • Only force acting on the object is the force due to gravity • Object is accelerating vertically (downward) at 9.8 m/s2 • Horizontal motion is independent of vertical motion. • Draw a picture and sort out the horizontal motion from the vertical motion. • Range is the horizontal displacement (x, r, d), height is the vertical displacement (y, h, d).

  13. Free fall and Projectile Motion

  14. Freefall A hot-air balloonist loosens a sandbag and lets it fall to the ground. If the balloon has an altitude of 200 m. How long before the sandbag hits the ground? What is its final velocity (right before it hits the ground)?

  15. Projectile Motion A hot-air balloonist throws some junk out of his basket. It has an initial horizontal velocity of 5 m/s. If the balloon has an altitude of 200 m. How long before the sandbag hits the ground? What is its final velocity (right before it hits the ground)? How far away from the balloon does it travel?

  16. Circular Motion • Caused by a centripetal force • Force and acceleration are directed inward along the radius of the circle • If you stop applying the centripetal force the object will fly off in a path tangent to the circle. • Angular speed is equal no matter what your radius is for a given rotation • The tangential velocity increases as you increase your radius (circle gets bigger)

  17. Circular motion A roller coaster loaded with passengers has a mass of 2.0 x 103 kg; the radius of curvature of the track at the lowest point of the track is 24 m. If the vehicle has a tangential speed of 18 m/s at this point, what force is exerted on the vehicle by the track?

  18. Gravitation • Between 2 masses • This includes person standing on a planet (distance = radius) • Can be found with either the “big equation” or F=mg depending on the information you are given.

  19. Gravitation A set of physics textbooks weighs 294 N on earth, what would they weigh on a planet that has ½ the mass and ½ the radius of earth?

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