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Motion Which unit is used to measure distance? centimeters An athlete is running a 5-km race at an average speed of 8 km/h. She has to stop to tie her shoe. After tying her shoe, she continues running at 8 km/h. Why would her average speed for the entire race be less than 8 km/h? The total time she took to complete the race increased because she stopped. An elevator traveled 15 floors (150 ft) at a speed of 4.5 m/s. What additional information is needed to determine the velocity of the elevator? The direction the elevator traveled. Which of the following is a definition of motion? A change in position over time. Three runners compete in a 400-m race on an oval-shaped running track. At a certain time, one runner is 15 m behind the finish line. Which term describes the finish line? reference point Montez read that bobcats can reach speeds of up to 30 mi/h. What does the speed of a bobcat indicate? The distance it can travel in a certain amount of time . Tyrone wants to determine how fast a bowling ball travels when it is bowled. He uses a stopwatch to record, in seconds, the time it takes for the bowling ball to reach the pins. Which unit would be most appropriate to measure the length of the bowling lane? meters What would be best measured in kilometers? The distance a plane travels during flight What is acceleration? The rate at which velocity changes An airplane leaves New York to fly to Los Angeles. It travels 3,850 km in 5.5 hours. What is the average speed of the airplane? 700 km/h Which is an example of acceleration? A bus moves on a straight road and then makes a right turn. Which is an example of centripetal acceleration? An object moving in a circle at20 m/s. Which of the following describes an object moving in a circle steadily? Change in direction only. Which scenario does not describe an example of acceleration? A car maintains a constant speed while driving straight ahead Julia is in a car with her father. The car is undergoing centripetal acceleration. What is happening to the car? The car is changing direction at a constant speed. In order for a space shuttle to leave Earth, it must produce a great amount of thrust. Its rocket boosters create this thrusting force by burning great amounts of fuel. However, once in space, the shuttle needs very little fuel. It circles Earth while gravity pulls it toward Earth. What term describes the motion of the shuttle around Earth? orbit High and low tides are the regular pattern of rising and sinking ocean-water levels. They are formed as a result of the gravitational forces of the moon and sun on Earth’s oceans. The moon has a greater effect on Earth’s oceans than the sun. Why would the moon have a greater effect than the sun? The moon is closer to Earth than the sun is. What is gravity? The force that pulls all objects toward one another. Two objects have a certain gravitational force between them. What would happen if the mass of one of the objects suddenly increased? The gravitational force between the two objects would increase. Melanie watched the path a baseball followed after a pitcher threw it. She noticed that the ball traveled horizontally away from the pitcher, as well as downward toward the ground. What force caused the ball to accelerate in the downward direction when it was thrown? gravitational force A skydiver jumps out of a plane. She falls downward at a very fast speed. When she opens her parachute, she slows down. What force pulled the skydiver to the ground? gravity Which of the following would exert the greatest gravitational force on a body? A planet