Force and Motion 8 th Grade Science Mrs. Howald

Today in Science: Explain that an unbalanced force acting on an object changes that object's speed and/or direction. Main Idea: How have our ideas changed since the Greeks started studying motion? Log Updates: 22.Log sheet #3 23.Inertia power point notes Homework: Reflection (above)

Vocabulary Updates Force –a push or pull Friction – a contact force that opposes motion and occurs when a moving object rubs against a surface Mass – amount of matter that an object contains Inertia –tendency of an object to remain at rest or in motion until acted upon by an external force

Describe how the change in the position (motion) of an object is always judged and described in comparison to a reference point Main Idea: When we describe the location of any object, it is necessary to refer to other objects in the same area. This is an example of a “reference point”.

Where is it? Describe the location of some object in the classroom. Write your description on a piece of paper. Give your description to another student (without the answer) After receiving a description from another student, try to find the object described on another student’s paper—write your answer at the bottom of the page

Describe how the change in the position (motion) of an object is always judged and described in comparison to a reference point. Main Topic: What is the difference between distance and displacement? –Check understanding of reference points –Washer Activity –Discussion –Vocabulary Words Homework: distance and displacement worksheet – due tomorrow

Describe how the change in the position (motion) of an object is always judged and described in comparison to a reference point. Main Topic: Relative Motion and Frame of Reference –Review homework –Videos –Discussion –Read pp and answer ??

Relative Motion http:// 0

Reminder (Previous cycle): Distance and Displacement START FINISH Need to distinguish how long we traveled from how far away (and in what direction) we traveled.

Distance and displacement Distance and displacement are two quantities which may seem to mean the same thing, yet have distinctly different definitions and meanings. Distance refers to "how much ground an object has covered" during its motion. Displacement refers to "how far out of place an object is"; it is the object's change in position.

Vocabulary Position –the description of where an object is in space Direction –the line or path along which an object moves

Vocabulary Frame of reference (reference point) – a stationary object against which motion is measured Motion – the change in position of an object with respect to time Relative Motion – the motion of one body relative to another. Please add this word to your list!!

Force and Motion -- Log Sheet Force and Motion Log Sheet Updates 1.October Class Notes 2.Vocabulary Page 3.Distance and Displacement Worksheet 4.The Traveling Washer Review Worksheet 6.Race Car Lab Worksheet 7.Practice Worksheet -- Speed

8. Calculating average speed 9. Graphing Distance VS Time 10. Motion Graphs 11.Reflection #2 12.Calculating speed, distance, and time

Explain that motion describes the change in the position of an object (characterized by a speed and direction) as time changes. Main Topic: Determining Speed –Lab Reports –Pop Quizzes –Race Car Lab –Discussion –Homework: Complete the Practice Worksheet -- Speed

Explain that motion describes the change in the position of an object (characterized by a speed and direction) as time changes. Main Topic: Constant Speed, Average Speed, Instantaneous Speed Review data from yesterday – make graphs on the floor Discuss speed and the unit of measure for speed Review worksheet from yesterday – make corrections Practice worksheet for constant speed graph Vocabulary

Spring 2005 Data Video 2

Vocabulary Speed –the distance an object moves in a certain time period speed = distance time Constant Speed – Moving equally fast all the time.

Average vs. Instantaneous speed Add these words to your list Average speed is the distance traveled divided by the time to travel. Instantaneous speed is the average speed for infinitely small distances and times.

Explain that motion describes the change in the position of an object (characterized by a speed and direction) as time changes. Main Topic: Calculate Speed, Distance, or Time. Daily Review S/D/T relationship and formulas Practice Problems Vocabulary Homework: Complete the other side of the Calculating Speed Worksheet – word problems for speed, distance and time. The last two are “extra credit”.

Understanding Speed

Acceleration and Deceleration (Negative Acceleration)

screen-stopwatch/ Main Topic: How forces affect motion –Check homework –Outline –Study Guide –Videos –Homework – quiz on Friday – review study guide.

Vocabulary Velocity – the speed of an object in a particular direction Acceleration – a change in velocity Motion – the change in position of an object with respect to time

Aristotle and Motion Idea that force causes motion goes back to the fourth century B.C.E. -- Greeks Divided into two types: –Natural Motion –Violent Motion

Aristotle and Motion Natural Motion –Up or Down –Objects seek a natural resting place -- boulders/ground smoke/high –Circular motion is “natural” for the heavens. Planets and Stars revolve around Earth

Aristotle and Motion Natural Motion –Since they are natural, they are not caused by forces.

Aristotle and Motion Violent Motion –Imposed Motion – a push or a pull –External Cause –Objects in their natural resting places could not move without a push or a pull –If an object is moving “against its nature” then a force is responsible

Ideas About Motion These ideas were believed for over 2000 years.

Copernicus First to say that the Earth moved around the Sun. Worked in secret

Galileo A force is necessary to keep an object moving

Galileo Force = any push or pull Friction = the force that acts between materials that touch as they move past each other

Galileo Friction – if friction were absent, a moving object would need no force to stay in motion

Galileo

If an object is moving, it is “natural” to keep moving. Every object resists change to its state of motion.

Galileo Inertia – the property of a body to resist change

Newton – Laws of Motion The first law (law of inertia) is a restatement of Galileo’s idea.

Friction and Inertia

Newton – Newton’s First Law: –Every object continues in a state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by forces exerted upon it.

Newton – Simply put: –Things keep doing what they are already doing.

Objects At Rest

Objects in Motion

In Review Inertia gives us a completely different view of motion. Ancients thought – continual forces were needed to keep something in motion We now know that objects continue to move by themselves Forces may be needed to overcome friction and set things into motion at first. Once an object is moving in a force free environment, it will move in a straight line indefinitely.

Mass – A Measure of Inertia Kick and empty can and it moves Kick a can filled with sand and it does not move as much Kick a can filled with nails and you’ll have a sore foot Inertia: –Can full of nails = most –Can full of sand = less –Empty can = least

Mass – A Measure of Inertia Kick and empty can and it moves Kick a can filled with sand and it does not move as much Kick a can filled with nails and you’ll have a sore foot Inertia: –Can full of nails = most –Can full of sand = less –Empty can = least

Mass – A Measure of Inertia The amount of inertia an object has depends on its mass—the amount of material present in an object.

Mass – A Measure of Inertia The more mass an object has… The more inertia it has… The more force it takes to change its state of motion

Mass is not volume

Mass is not weight

Mass and weight are proportional to each other In the same location, twice the mass means twice the weight Objects with great mass have great weight Objects will little mass have little weight

Measuring Mass and Force

Effects of Forces on Speed

Log Sheet 13.Motion Notes – power point 14.Speed Worksheet 15. Motion Outline 16.Study Guide – Motion Quiz