# Ummm…Isn’t that thing in the bag an accelerometer?

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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. 0123123

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) 0 1 2 3 1 2 3

Are you correct? F GPE F NPS 0 1 2 3 1 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: 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) 0123123

Are you correct? F GPE F NPS 0123123

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) 0 123123

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

Are you correct? 0123123 F GPE F NPS F PPS

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 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) Draw a force diagram for the rider. (13) 0 1 2 3 1 2 3 v FF a

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

OMG example On the Ninja, a 45 kg rider goes upside- down 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) 0 1 2 3 1 2 3 v FF a

Frame of Reference Check 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) 0 1 2 3 1 2 3

Are you correct? F GPE F NPS 0 1 2 3 1 2 3 Can you calculate the net force on the rider? The acceleration of the rider ?

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