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TAKS Objective 5

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TAKS Objective 5

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    1. TAKS Objective 5 Forces, Speed, Acceleration And Momentum

    2. Law of Conservation of Energy Energy can change forms, but is never created nor destroyed Loss in one form = gain in an another form A falling object speeds up as it falls to the ground; PE decreases as KE increases. The KE it has at impact = the PE it had before it fell.

    3. Motion can be described as a change in an object’s position Average velocity (speed) is the change of position (distance) of an object over time

    4. Definition of a Force A Force is a push or a pull

    5. Velocity Graphs V = distance time Velocity (v) is the slope (rise over run) of a distance (d) vs. time (t) graph

    7. 4 The picture shows the position of a ball every 0.25 second on a photogram. Using a ruler, determine the velocity of the ball.

    8. Acceleration is a change in an object’s velocity (speed or direction) When an object’s speed changes over time it is accelerating (or decelerating) A = vfinal – vinitial time Units for acceleration m/s/s or m/s2

    9. Acceleration Graphs Acceleration (a) is the slope of a velocity (v) vs. time (t) graph When plotted on a distance vs. time graph, acceleration is an exponential curve

    10. Read the graph first, what is each segment telling you? 41 According to this graph, what was the bicycle’s acceleration between 6 and 10 seconds? A 0.0 m/s2 B 0.65 m/s2 C 1.6 m/s2 D 6.5 m/s2

    11. Balanced Force A force that produces no change in an object’s motion because it is balanced by an equal, opposite force. If you were to add these forces they would = 0If you were to add these forces they would = 0

    12. Unbalanced Forces Are forces that results in an object’s motion being changed. Add together to equal greater force.Add together to equal greater force.

    13. Remember to read diagrams first! What happened in the pictures? Now read the question . . . 32 Starting from rest at the center of a skating rink, two skaters push off from each other over a time period of 1.2 s. What is the force of the push by the smaller skater? F 16 N G 32 N H 88 N J 100 N

    14. Friction A force that acts in a direction opposite to the motion of two surfaces in contact with each other.

    15. Friction Friction causes an object to slow down and stop. Since the amount of energy stays constant, the energy becomes heat. To reduce friction oil or other lubricants are used. Air resistance is an another example of friction. Lubricants or grease reduce friction.Air resistance is an another example of friction. Lubricants or grease reduce friction.

    16. F A constant force on an object produces a constant positive acceleration. G An object in motion tends to remain in motion in the absence of an external force. H A moving object having constant velocity contains kinetic energy. J An object’s weight is proportional to its mass.

    17. Momentum = Mass x Velocity The larger the mass OR the faster an object moves, the more momentum it has. That means it will hit harder, or do more damage. If a penny is thrown it probably won’t hurt very much, but if it is shot from a sling shot with a higher velocity, it will hurt a lot!

    18. 27 A ball moving at 30 m/s has a momentum of 15 kg·m/s. The mass of the ball is — A 45 kg B 15 kg C 2.0 kg D 0.5 kg

    19. Newton’s 1st Law of Motion Objects in motion stay in motion And objects at rest stay at rest Until they are acted upon by an unbalanced force.

    20. Inertia or Newtons 1st Law Tendency for an object to stay at rest or moving in a straight line at a constant speed. The mass (m measured in kg) of an object determines its inertia Inertia comes from the Latin word meaning lazy. Inertia comes from the Latin word meaning lazy.

    21. Newton’s 2nd Law of Motion The greater the force applied to an object, the greater it will accelerate. Force = Mass X Acceleration or F=ma

    22. Newton’s 2nd Law of Motion The greater the mass of an object, the greater the force required to change its motion.

    23. Newton’s 2nd Law of Motion The greater the acceleration of an object, the greater the force required to change its direction of motion.

    24. Weight force of gravity on an object is a commonly measured force. It is calculated by F=mg, where g is the acceleration due to gravity. g = 9.8 m/s2 (found at the bottom of the equation page)

    25. 20 How many Newtons of force does a 70.0 kg deer exert on the ground because of gravity? Record and bubble in your answer on the answer document. This is an example of a weight problem since the force is due to gravity. F = mg or = 70kg x 9.8m/s/s = 686 Newtons

    26. Example 2nd Law Problem 18 What is the net force exerted on a 90.0 kg race-car driver while the race car is accelerating from 0 to 44.7 m/s in 4.50 s? F 9.8 N G 20 N H 201 N J 894 N

    27. Newton’s 3rd Law of Motion For every action force there is an equal and opposite reaction force.

    28. Newton’s 3rd Law of Motion All forces come in action-reaction pairs Ex: feet push backward on floor, the floor pushes forward on feet

    29. Example of the 3rd Law: 52 When the air is released from a balloon, the air moves in one direction, and the balloon moves in another direction. Which statement does this situation best illustrate? F What goes up must come down. G For every action there is an equal and opposite reaction. H The shape and size of an object affect air resistance. J The acceleration due to Earth’s gravity is 9.8 m/s 2.

    30. Your Turn!! 1. A 0.50 kg ball with a speed of 4.0 m/s strikes a stationary 1.0 kg target. If momentum is conserved, what is the total momentum of the ball and target after the collision? A 0.0 kgm/s B 0.5 kgm/s C 1.0 kgm/s D 2.0 kgm/s

    31. 2. The table contains data for two wrecking balls being used to demolish a building. What is the difference in momentum between the two wrecking balls? F 300 kgm/s G 200 kgm/s H 150 kgm/s J 0 kgm/s

    32. Be careful: what is the thickness referring to? 3. The speed of sound in human tissue is about 1600 m/s. If an ultrasound pulse takes 1.5 × 10 – 5 s to travel through a tissue, what is the thickness of the tissue? F 2.4 km G 2.4 m H 24 cm J 24 mm

    33. 4. The pictures show how an air bag functions in a collision. How much momentum in kg m/s does the air bag absorb from the crash-test dummy if all the crash-test dummy’s momentum is absorbed by the air bag? Record and bubble in your answer to the nearest whole number on the answer document.

    34. 5. The picture above shows the directions in which water leaves this scallop’s shell. Which picture below shows the direction the scallop will move?

    35. And the answers are: D: use the formula page, mass x velocity J: again, mass x velocity, they are both 300 kgm/s. J: v=d/t so 1600m/s x 1.5 x 10-5 =.024m which is 24 mm Momentum = mass x velocity or 5.5 x 100 or 550 kgm/s. D: For each action an equal opposite reaction, since the force is out and down, the shell will move up.

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