Terminology • Motion is the changing distance of an object compared to another object • Reference points are places or objects used to determine if an object is in motion • Relative motion is dependent on the reference point(s) used • International System of Units (SI) is a universal system of measurement used by scientists throughout the world • Base units include: length(m), weight (kg), volume (L)

- Describing and Measuring Motion Measuring Distance • You can measure distances shorter than 1 meter in centimeters. The wingspan of the butterfly is 7 cm.

Use a conversion factor to convert one metric unit to another. A conversion factor is a fraction in which the numerator and denominator represent equal amounts in different units. Multiply the number you want to convert by the conversion factor. Suppose you want to know how many millimeters (mm) are in 15.5 meters (m). Since there are 1,000 millimeters in 1 meter, the conversion factor is: 1,000 mm/1 m Multiply 14.5 meters by the conversion factor to find millimeters. 14.5 m X 1,000 mm/1 m = 14.5 X 1,000 mm = 14,500 mm - Describing and Measuring Motion Converting Units

Practice Problem How many centimeters are in 22.5 meters? 22.5 m = 2,250 cm - Describing and Measuring Motion Converting Units

- Describing and Measuring Motion Calculating Speed • If you know the distance an object travels in a certain amount of time, you can calculate the speed of the object.

Speed = Distance / Time • Average speed = Total Distance / Total time • Instantaneous Speed = the rate an object is moving at a given instant in time • Velocity is the measure of both speed and direction of an object’s motion • Slope = rise / run • *the slope of a graph tells you how fast one variable changes in relation to the other variable in comparison (rate of change)

- Describing and Measuring Motion Graphing Motion • You can show the motion of an object on a line graph in which you plot distance versus time.

- Describing and Measuring Motion Using Prior Knowledge • Before you read, write what you know about motion in a graphic organizer like the one below. As you read, write what you learn. What You Know A moving object changes position. Objects move at different speeds. What You Learned Motion is compared to a reference point. The SI unit of length is the meter.

End of Section:Describing and Measuring Motion

- Slow Motion on Planet Earth Earth’s Plates • According to the theory of plate tectonics, Earth’s landmasses have changed position over time • because they are part of plates that are slowly moving.

- Slow Motion on Planet Earth Plate Movement • Some plates move at a rate of several centimeters each year. Others move only a few millimeters per year.

- Slow Motion on Planet Earth Previewing Visuals • Before you read, preview Figure 8. Then write two questions that you have about the diagram in a graphic organizer like the one below. As you read, answer your questions. Previewing Figure 8 Q. How have the positions of the continents changed over time? A. The distance between the continents has increased. Q. What causes Earth’s plates to move? A. Slow-moving currents beneath Earth’s outer layer cause the plates to move.

End of Section:Slow Motion on Planet Earth

Acceleration • Acceleration is the rate at which velocity changes. • Remember that velocity involves both speed & direction! • Therefore, a change in velocity can therefore involve either speed or direction. • Increasing speed = acceleration • Decreasing speed = acceleration (deceleration) • Changing direction = acceleration

- Acceleration Calculating Acceleration • To determine the acceleration of an object moving in a straight line, you must calculate the change in speed per unit of time.

As a roller-coaster car starts down a slope, its speed is 4 m/s. But 3 seconds later, at the bottom, its speed is 22 m/s. What is its average acceleration? Read and Understand What information have you been given? Initial speed = 4 m/s Final Speed = 22 m/s Time = 3 s - Acceleration Calculating Acceleration

As a roller-coaster car starts down a slope, its speed is 4 m/s. But 3 seconds later, at the bottom, its speed is 22 m/s. What is its average acceleration? Plan and Solve What quantity are you trying to calculate? The average acceleration of the roller-coaster car = __ What formula contains the given quantities and the unknown quantity? Acceleration = (Final speed – Initial speed)/Time Perform the calculation. Acceleration = (22 m/s – 4 m/s)/3 s = 18 m/s/3s Acceleration = 6 m/s2 The roller-coaster car’s average acceleration is 6 m/s2. - Acceleration Calculating Acceleration

As a roller-coaster car starts down a slope, its speed is 4 m/s. But 3 seconds later, at the bottom, its speed is 22 m/s. What is its average acceleration? Look Back and Check Does your answer make sense? The answer is reasonable. If the car’s speed increases by 6 m/s each second, its speed will be 10 m/s after 1 second, 16 m/s after 2 seconds, and 22 m/s after 3 seconds. - Acceleration Calculating Acceleration

Practice Problem A falling raindrop accelerates from 10 m/s to 30 m/s in 2 seconds. What is the raindrop’s average acceleration? (30 m/s – 10 m/s) ÷ 2 seconds = 10 m/s2 - Acceleration Calculating Acceleration

Practice Problem A certain car can accelerate from rest to 2.7 m/s in 9 seconds. Find the car’s average acceleration. (27 m/s – 0 m/s) ÷ 9 s = 27 m/s ÷ 9 s = 3 m/s2 - Acceleration Calculating Acceleration

- Acceleration Graphing Acceleration • You can use both a speed-versus-time graph and a distance-versus-time graph to analyze the motion of an accelerating object.

- Acceleration Identifying Main Ideas • As you read the section “What is Acceleration?”, write the main idea in a graphic organizer like the one below. Then write three supporting details that further explain the main idea. Main Idea In science, acceleration refers to... Detail Detail Detail Increasing speed Decreasing speed Changing direction

End of Section:Acceleration

Graphic Organizer Motion is described relative to a is measured by Reference point Distance ÷ Time in a given direction is called equals Speed Velocity

End of Section:Graphic Organizer

Table of Contents