Table of Contents Describing and Measuring Motion Slow Motion on Planet Earth Acceleration

Merry-go-round

Family Road Trip

Describing Motion - Describing and Measuring Motion Whether or not an object is in motion depends on the reference point you choose.

Heliocentric Model of our Solar System

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)

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

Converting Units - Describing and Measuring Motion 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

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

Calculating Speed - Describing and Measuring Motion 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)

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

Using Prior Knowledge - Describing and Measuring Motion 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

Earth’s Plates - Slow Motion on Planet Earth 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.

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

Previewing Visuals - Slow Motion on Planet Earth 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! A change in velocity can therefore involve either speed or direction: Increasing speed = acceleration Decreasing speed = acceleration (deceleration) Changing direction = acceleration

*Why are zero speed and zero acceleration not the same? *Zero speed = no motion *Zero acceleration = no change in motion An object that is not accelerating can still be moving at a constant speed in a constant direction! An object with no speed is not in motion!

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. Acceleration = Final speed – Initial speed / Time

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? Read and Understand What information have you been given? Initial speed = 4 m/s Final Speed = 22 m/s Time = 3 s

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/3 s Acceleration = 6 m/s2 The roller-coaster car’s average acceleration is 6 m/s2.

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.

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

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

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.

Is this object accelerating? If so, by how much?

A curved line shows that the object is accelerating!

Identifying Main Ideas - 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 Reference point Distance ÷ Time Speed 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