170 likes | 266 Vues
Learn how force factor meters, not accelerometers, measure forces and acceleration. Discover how to interpret readings and calculate forces accurately. Includes examples and explanations.
E N D
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 3 2 • 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) 1 0 1 2 3
Are you correct? 3 2 FNPS 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: • 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) 3 2 1 0 1 2 3
Are you correct? FNPS 3 2 1 0 1 2 3 FGPE
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 3 2 1 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 3 2 1 0 1 2 3 FGPE
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 2 • 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) 1 SF 0 a 1 v 2 3
Are you correct? 3 2 • Can you calculate the net force on the rider? The acceleration of the rider? 1 0 FGPE 1 2 3
OMG example 3 2 • 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) 1 SF 0 a 1 v 2 3
Frame of Reference Check 3 2 • 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 3
Are you correct? 3 2 FGPE • Can you calculate the net force on the rider? The acceleration of the rider? 1 0 FNPS 1 2 3