Describing Motion Mrs Wolfe Motion Describe the motion

Describing Motion Mrs. Wolfe

Motion • Describe the motion of these wind-up toys. • How far does it move? • How fast does it move? • Does it move at a steady rate, speed up, or slow down? • What direction does it move? • These all describe MOTION.

Motion • Distance – total change in position • Displacement – change in POSITION in a STRAIGHT LINE

Problem: Is your desk in motion? • We need a reference point… – Reference point – nonmoving point from which motion is measured

Reference Point • Motion – Change in position in relation to a reference point. Reference point Motion

Problem: You are a passenger in a car stopped at a stop sign. Out of the corner of your eye, you notice a tree on the side of the road begin to move forward. You have mistakenly set yourself as the reference point.

Speed • Speed – the rate at which an object changes its position • What is your speed if you cover 240 miles in 4 hours? • Never Fear! Equation person is here!

Speed = Distance/Time • S = d/t • What is your speed if you cover 240 miles in 4 hours? • S = 240/4 = 60 mi/hr!!

Units in Your Answer • Example units – Seconds, Minutes, Hours – Miles, Feet, Meters – Miles/Hour, Feet/Second • Units are IMPORTANT! • There’s a BIG difference between 60 miles/hr and 60 miles/sec…

Problem: • What is the speed of a car moving 124 miles in 2 hours? • SHOW EQUATION, correct answers, and units!

ANSWER • S = d/t • 124/2 = 62 mi/hr

Let’s practice with a worksheet! d v t

DEMO – MEASURING SPEED • CONSTANT SPEED VEHICLE • Measure distance in METERS • Measure time in SECONDS • How do I figure it out? • Let’s do the MATH!!

Time for a LAB!! Are there speeders on Havens Corners Rd. ?

Do you REALLY understand? … • Pretend that the speedometer on your car is broken. • How could you figure out how fast you’re going?

During a trip, you have… • Average speed – • You travel from Columbus to Cincinnati (220 miles) in your average speed 4 hours. over the whole trip – What is your speed? • Instantaneous – Did you have this speed throughout the entire speed – your speed at any given trip? NO! It’s your AVERAGE speed. instant during the – What was your trip instantaneous speed at a stop sign?

Back to Equation Person! • S = d/t • What type of speed are you calculating with this equation? Instantaneous or Average? • DEMO: http: //www. physicsclassroom. com/ mmedia/kinema/trip. html

Problem: A storm is 10 km away and is moving at a speed of 60 km/h. Should you be worried? It depends on the storm’s direction!

Velocity • Velocity is speed with a DIRECTION. • Example: 70 mph is a speed. 70 mph North is a velocity.

Problem: • A plane flies at a speed of 720 mi/hr from Columbus to Indianapolis. • What is the average speed of the plane? • 720 mi/hr • What is the average velocity of the plane? • 720 mi/hr WEST

DEMO • Two students walking… • Do they have the same speed? Velocity? • How would they have to move to have BOTH the same speed & velocity?

Problem: How Fast Does Earth Move? • Earth rotates 25, 488 miles counterclockwise in 24 hours. How fast does Earth rotate? – SHOW EQUATION, ANSWER, UNITS! – Is this speed or velocity?

Let’s practice with a worksheet!

Changing Velocity • Sometimes objects CHANGE velocity as they move. • Demo: Roll car down a ramp. How is its velocity CHANGING? • This is known as ACCELERATION!

Acceleration Demo • http: //www. physicsclassroom. com/mmedia/ kinema/acceln. html

How else can you accelerate (without changing your speed)?

Acceleration • Acceleration is a change in VELOCITY due to a change in direction or speed. • Speed up • Slow down • Change direction

Time for a LAB!! Building Accelerometers!!

ACCELERATION IS A RATE OF CHANGE in velocity!!

Equation Person Returns! • Your engine shuts off and you slow down from 60 mph to 0 mph in 3 seconds. What is your acceleration? a: • What are the units of your vf: acceleration? v i: t: acceleration final velocity initial velocity time

ANSWER • A = 0 – 60 3 • -20 mi/hr/sec vf - vi a t

NEGATIVE Acceleration? ? • Positive acceleration – “speeding up” • Negative acceleration – “slowing down” – That makes sense, since we went from 60 0 !!

Let’s practice with a worksheet!

Time for a LAB!!