Physical Science: Ch 11 Notes

1. A. Speed and Velocity • Average speed – is the total distance traveled divided by the time it takes to travel that distance. Physical Science: Ch 11 Notes • During the time an object is moving, its speed may change, but this equation tells you the average speed over the entire trip. Instantaneous speed – the rate at which an object is moving at a given moment in time. This is difficult to measure without technology like a speedometer. • The metric unit for speed is “meters per second” or m/s. • The slope of a line on a distance-time graph is speed. A steeper slope on a distance-time graph indicates a higher speed.

2. Practice Problems: • What was the speed of a turtle if it traveled 1 meter in 10 seconds? • What was the speed of a student who walked 40 meters in 24 seconds? • What was the speed of a student who took 10 seconds to move just 2 meters? • If a Corvette travels at a speed of 5 m/s, how many meters will it travel in 135 seconds? Physical Science: Ch 11 Notes Velocity – the speed and direction in which an object is moving. • The metric unit for velocity is “meters per second” or m/s and it is sometimes followed with a direction like “right” or “north”. • A change in velocity can be the result of a change in speed, a change in direction, or both.

3. Practice Problems: • A deer is moving east to cross a highway. If the deer is moves 64 meters in 8 seconds, what is the velocity of the deer? • A mailman is driving up a hill. If his car travels 45 meters in 15 seconds, what is his velocity? • If Mrs. Casey runs east with a velocity of 7 m/s for 200 seconds, how many meters will she travel (and in what direction)? Physical Science: Ch 11 Notes

4. B. Acceleration – the rate at which velocity changes • -change in speed = acceleration • -change in direction = acceleration • -change in both speed and direction = acceleration • You calculate acceleration for straight-line motion by dividing the change in velocity by the total time. Physical Science: Ch 11 Notes • The metric unit for acceleration is “meters per second per second” or “meters per second squared” (m/s/s or m/s2) • If the velocity increases, the acceleration is a positive value. If the velocity decreases, the acceleration is a negative value (called deceleration).

5. Practice Problems: • A sled begins at rest (0 m/s) at the top of a hill. If the sled reaches the bottom of the hill 9 seconds later with a velocity of 7 m/s, what was the acceleration of the sled? • Mr. Swenson is in a hurry to get to home. If he is initially traveling at 40 m/s but stomps on the gas and 6 seconds later is traveling at 55 m/s. What was his acceleration? • Mark has to slow down a bit as he runs up a hill for cross country. If he was initially running 7 m/s but slowed down to 5 m/s about 10 seconds later, what was his acceleration? Physical Science: Ch 11 Notes

6. Constant acceleration – a steady change in velocity. This occurs when the velocity of an object changes by the same amount each second. • Free fall – the constant acceleration of a falling object due to the Earth’s gravity. • Objects falling near Earth’s surface accelerate downward at a constant rate of 9.8 m/s2. • Each second an object is in free fall, its velocity increases by 9.8 m/s. • This increase in velocity is constant for all objects falling to earth, no matter their mass, size, or shape (but air resistance makes it appear that heavier objects fall faster). Physical Science: Ch 11 Notes