Physics: TAW
Peter Baker
Activity 2.2.1:
Galileo analysed projectile motion and found that it could be split into two separate
components: an x component and a y component. These would represent the horizontal and vertical
axes respectively. In traditional projectile motions, these were independent of each other, related
only by the parameter of time.
He showed that the motion of a projectile was a parabola, assuming constant conditions. In
this way, he pushed the idea that physics was linked directly to mathematics, and that “the proper
language of nature is mathematics.” This, he said, was the only way we would be able to develop
knowledge of our world.
Activity 2.4:
Conditions during the launch of a rocket:
The g forces experienced by an astronaut being launched in a rocket are large enough that
conditions have to be taken into consideration. One thing that is done is that the shorter axis of
the body is placed in the direction of motion, so that the effects on the body and the alertness of
the people on board is maintained. This means that the astronauts are basically lying down for
the launch of a rocket directly into the air. If the longer axis is placed in line with the direction of
motion, then the blood can pool in the bottom of the body, creating problems from lack of blood
to the top of the body, especially the brain. It can result in things such as blackouts, dizziness,
lack of alertness, and of course, problems with arteries and things bursting.
Definition of “g forces”:
“G forces” were initially used to describe the effects on pilots and astronauts when in motion
during their jobs. The intended frame of reference is such that it does not include everyday
things such as sitting at home (where one could say one was pulling “+1G”). Nor is it to be used
for zero gravity situations.
It is useful for its original purpose, because it can be used to work out how much pressure or
force a person will be able to take on their body before something bad happens, eg loss of
consciousness…
For example, if a pilot is pulling out of a dive, he might have an acceleration of 3g’s up,
because of the centripetal acceleration. He feels like he is being pushed down into the seat, but
the forces are actually pushing the seat up into him. If we then add the (constant) acceleration
due to gravity, we can see that the total “g forces” on the pilot is actually 4g’s. We call this
“+4G’s” or a reaction force of “4W”. People also use the terminology “pulling 4G’s”.
Forces on an astronaut during launch:
The speed of a rocket leaving the earth has to be such that it exceeds the escape velocity of the
earth, which is 11200ms-1. This obviously requires a lot of acceleration, since the rocket starts at
a velocity of 0ms-1. Therefore, it works out that the rocket needs to accelerating about twice the
gravity of the earth in order to reach this velocity. This adds +2G’s to the gravity of the earth,
and therefore we can see that the resultant effect will be +3G’s, or a force of 3W.
Activity 2.4.1:
When a rocket is sitting on the launch pad, it is already moving relative to a viewer who is
stationary and situated externally to the earth. There are two motions: the orbital motion of the
earth as it rotates around the sun, and also the rotational motion of the planet.
The creates problems when we are trying to aim rocket as at planets far away. Small
inaccuracies could make for a lot of fuel being spent that doesn’t need to be. Therefore, we need to
account for these two motions when we launch rockets in order to save on fuel.
It is similar to the example of dropping something out the window of a moving car. It is
(initially) moving forward at the same rate as the car, however, to the people in the car (probably a
car full of hoons…) it would appear to be dropping vertically (initially).