Suited for Spacewalking pdf - Virtual Astronaut

Exploration BriefDifferent GravityContextGravity is an attractive force that all objects have forone another. It doesn't matter whether the object isa planet, a cannon ball, a feather, or a person. Eachexerts a gravitational force on all other objectsaround it.The amount of the gravitational force between twoobjects is directly proportional to the product oftheir two masses and inversely proportional to thesquare of the distance between their centers ofmass.This relationship is expressed in the equationbelow. M1 and M2 are the respective masses of thetwo objects and r is the distance between their centersof mass. G is the gravitational constant.f = G m 1m 2r 2By referring to this equation, we can see that thef o rce of gra v i ty is not con s t a n t . The amountdepends upon local conditions. For example, anastronaut walking on the surface of the Moonwould weigh only 1/6th what he or she wouldweigh on the surface of Earth.That same astronautwould weigh about 2/5ths as much on the surface ofMars. The reason for the difference is that theMoon and Mars are less massive bodies than Earthand they have smaller radii. Less mass reduces theamount of gravity experienced on the surface of theMoon and Mars while the smaller radii increases it.Besides being altered by mass and distance, our perceptionof gravity's pull can also be altered bymotion. Gravity can be made to appear to increaseby accelerating away from Earth, as in a rocketliftoff or by riding on a centrifuge. Gravity can bemade to appear to decrease by falling. NASA callsthe environment created by falling microgravity.You can get an idea of how this works by looking atthe diagram on the next page. Imagine riding in anelevator to the top floor of a very tall building. Atthe top, the cables supporting the car break, causingthe car and you to fall to the ground. (In this example,we discount the effects of air friction on thefalling car.) Since you and the elevator car arefalling together, you feel like you are floating insidethe car. In other words, you and the elevator car areaccelerating downward at the same rate due to grav-Suited for Spacewalking An Activity Guide for Technology Education, Mathematics, and Science, EG-1998-03-112-HQ • 6 3