How To Measure Acceleration UmmmIsnt that thing in

How To Measure Acceleration Ummm…Isn’t that thing in the bag an accelerometer?

How does that tube thing work? �It’s called an accelerometer, but it doesn’t really measure acceleration. 3 2 1 0 1 2 3

A clue to what it measures �Turn the tube so that it is vertical. Now it is measuring along the “head-to-toe axis. ” When you stand motionless, the tube looks like this: �What does that reading of “ 1” mean? �Draw a force diagram for a person standing motionless. (2) �How big is the normal force on the person by the floor compared to the force of gravity on the person by the earth? (3) 3 2 1 0 1 2 3

Are you correct? FNPS 3 2 1 0 1 FGPE 2 3

A Simple Confirmation of what that device tells you �Stand still. Hold the tube so that one end points directly in front of you. The device is now measuring along the “front-to-back” axis. The tube looks like this: 3 2 1 0 1 2 3 �On your force diagram for a person standing motionless, how big is the force pushing forward or backward on the person compared to the force of gravity on the person? (4)

Are you correct? FNPS FGPE 3 2 1 0 1 2 3

A more correct name than “Accelerometer” �The device is actually a “Force Factor Meter. ” �The reading on the device will tell you the size of a push or pull force on you compared to the size of the force of gravity on you. �The key to using it correctly is understanding which force it is measuring. �After obtaining the force factor readings, acceleration can be found by examining a force diagram.

Easy example: �On Mr. Freeze, a 45 kg rider speeds up while moving to the right. Predict the direction of movement on the force factor meter. (5) 3 2 1 0 1 2 3

Example (continued) �The force factor meter looks like this while the rider accelerates. Draw a force diagram for the rider. (6) Check your neighbor! SF a v

Are you correct? FNPS FPPS FGPE 3 2 1 0 1 2 3

Find the acceleration! �The rider’s mass is 45 kg. How much does the rider weigh? (7) � The force factor meter reads 2. 2. How big is the forward push on the person by the seat? (8) �What is size of the net force acting on the person? (9) �What is the person’s acceleration? (10)

Bonus! �Hey—the guy sitting next to this rider had a mass of 90 kg. What do you think his force factor meter read? (11)

Tougher example 3 �On the Screamin’ Eagle, a 45 kg rider goes over the crest of a hill. The FF meter is held on the head-to-toe axis. Predict the reading on the meter. (12) 2 1 SF 0 a 1 v 2 3 �Draw a force diagram for the rider. (13)

Are you correct? 3 2 1 0 FGPE �Can you calculate the net force on the rider? The acceleration of the rider? 1 2 3

3 2 OMG example 1 SF 0 a 2 3 �On the Ninja, a 45 kg rider goes upsidedown at the top of a loop. The FF meter is held on the head-to-toe axis. Predict the reading on the meter. (14) �Draw a force diagram for the rider. (15) 1 v

3 2 3 �Before we go on, notice that from the rider’s inverted point of view, the FF meter is moving “down” towards his lap. �So this FF reading is for a force directed which way? (16) 1 0 1 2 Frame of Reference Check

Are you correct? FGPE 3 2 1 FNPS 0 1 �Can you calculate the net force on the rider? The acceleration of the rider? 2 3