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# OCR Physics A level question - Galileo and Aristotle. Watch

1. Hi there folks, I'm doing an OCR Physics A level past paper - the june 2010 one to be precise, and I don't have the markscheme. Does anyone have any idea how to answer this question:

"Explain how experiments carried out by Galileo overturned Aristotle's ideas of motion."

It's something to do with the ramp that Galileo pushed the weights down, but apart from that, I'm clueless.

Cheers anyway, if anyone can answer this I'd appreciate it.
2. I did the same paper last year- Spec A and I cant remember learning about galileo or aristotle????
3. Well Aristotle said that weight and speed are directly proportional when object are falling.

Legend has it that Galileo dropped weights down from the Leaning Tower of Pisa. But he probably did it through a ramp becuause it's slower. It showed that different weights fall at same rate.

I don't know what the question is looking for but that's what I know
4. Basically what Soup said above but to extend on that:- Galileo actually carried out experiments on this (dropping weights...) but Aristotle just assumed that objects that have a large mass will have a larger acceleration and objects which have a smaller mass will have a smaller acceleration..

Obviously this idea from Aristotle was overturned by Galileo because Galileo discovered through his experiemtns that all objects (no matter what their mass) accelerate when in free fall at 9.8m/s/s.
5. Thanks guys, much appreciated
6. (Original post by wibletg)
Hi there folks, I'm doing an OCR Physics A level past paper - the june 2010 one to be precise, and I don't have the markscheme. Does anyone have any idea how to answer this question:

"Explain how experiments carried out by Galileo overturned Aristotle's ideas of motion."

It's something to do with the ramp that Galileo pushed the weights down, but apart from that, I'm clueless.

Cheers anyway, if anyone can answer this I'd appreciate it.
Most of the ideas of Aristotle in physics were theoretical axioms postulated by him. He is also credited of writing the first textbook.He is also known as the father of deductive reasoning in physics. They might have had a general feeling of being true on the basis of observations. Two of such ideas were: 1. Heavier objects fall faster than lighter object. And 2. State of rest is a preferred state of an object and all other states, even of uniform motion in a straight line would require some kind of force or influence acting on it. Aristotle had the support of the then church. He also had a reputation because of his profound thought and his experiments on plants. I have read in one of the books that when Galileo wanted people to look into his telescope the moons of Jupiter. people refused saying that if Aristotle has not written about them (moons) in his book then they cannot be there. Although it is common experience that a leaf takes a lot of time to fall to the ground and the stone falls quickly. The law really referred to the fall only under gravity with all other influence removed. Galileo thought otherwise and basically he believed in experiments. He is rightly called Father of experimental physics. The famous experiment of allowing a feather and a coin to fall from Leaning tower of Pisa is not historically documented but is believed, that Galileo must have done other controlled experiment to conclude two objects fall at the same rate to the ground if other effects are eliminated or their influence neglected. Any one can verify by allowing two stones of varying sizes to fall any vertical distance and by noting that they fall to the ground simultaneously. Even you can do this experiment from leaning tower of Pisa with a small pebble and a sheet of paper crumpled enough to form a small paper ball and find that the moment of their reaching to the ground is not much different. One need not use very strong terms such as 'over turning' while comparing two great giants such as Aristotle and Galileo. One cannot say that Einstein overturned the ideas of Newton. Einstein's ideas reduce to those of Newton in certain circumstances and without Newton's ideas in their proper place Einstein would have not got his ideas. Similar is the case here. Aristotle's assertion about deductive reasoning is a recognized form of researching into new ideas. And indeed what Galileo tried to prove experimentally can be derived by deductive reasoning alone with the help of a thought experiment. We can take two objects one heavier labeled as H and other lighter labeled as L. Now we can assume Aristotle to be correct and accept that if they are allowed to fall H will fall faster as Aristotle has said. then we can tie them together and postulate that the combination would not fall as fast as H and not as slow as L. But we know that the combination being heavier than H must fall faster. Thus getting into a contradiction. This can be removed only if we assume that they both fall equally. Similarly the fact that if an object moves with constant speed in a straight line will continue to move so if no impressed force is acting upon it is very difficult to prove because of the ubiquitous friction. Galileo proposed a thought experiment to drive home this point. That is the experiment with two inclined planes from one of then slope a ball is allowed to roll and it should go to the same height if no friction is there. Now if we go on lowering the slope of the other inclined plane then the ball will travel more and more distance to reach the same height and when the second slope is zero it will never stop logically because it will never reach the same height. This is the law of inertia originally propounded by Galileo and then adopted by Newton. So this idea is again in contradiction to what Aristotle had written that even a state of uniform motion in a straight line would require some force to be acting upon it.
7. Quick question, Why can gravitational field lines never cross?
8. (Original post by wibel)
Quick question, Why can gravitational field lines never cross?
Cos then if they crossed the object placed at the point of intersection would then feel twice the force, I'm guessing?
9. (Original post by wibletg)
Cos then if they crossed the object placed at the point of intersection would then feel twice the force, I'm guessing?
I don't think that is it
10. aristotle also believed motion could only occur when an external agent was acting on the body but galileo proposed a ball rolling down a frictionless surface would carry on forever
11. (Original post by wibel)
Quick question, Why can gravitational field lines never cross?
Because, gravitational field lines are meant to show direction of gravitational force. If they cross, it means the force is acting in two directions at once. But this is impossible as all gravity is one force. One force cannot act in two directions at once
Because, gravitational field lines are meant to show direction of gravitational force. If they cross, it means the force is acting in two directions at once. But this is impossible as all gravity is one force. One force cannot act in two directions at once
Good explanation thank you
13. NEED URGENT HELP
this is the Q

A boy is swimming across a river 65 m wide. He is travelling through the water with an overall velocity 2.3 m/s. The current in the river has a velocity of 1.1 m/s parallel to the bank.

a) Sketch a vector triangle showing the two given vectors and a third vector velocity of the boy perpendicular to the bank
b) Calculate the velocity towards him to cross the river.

Im stuck on part (b) mainly, so is anyone able to help me?
14. (Original post by wibel)
NEED URGENT HELP
this is the Q

A boy is swimming across a river 65 m wide. He is travelling through the water with an overall velocity 2.3 m/s. The current in the river has a velocity of 1.1 m/s parallel to the bank.

a) Sketch a vector triangle showing the two given vectors and a third vector velocity of the boy perpendicular to the bank
b) Calculate the velocity towards him to cross the river.

Im stuck on part (b) mainly, so is anyone able to help me?
I think all you have to do is calculate the other side of the vector triangle, this time your are given the resultant. By using pythagors' theorem you are finding the third vector velocity which is the velocity towards him. We are given the current and the velocity he is swimming at. You should note that you want to work out a smaller side, and that its direction is at what degree's to the bank if it is perpendicular?
15. I do understand it and I sketched the diagram but i don't see how they got the answer. (Answer: 2.0 m/s at 90 degrees to the bank)
16. (Original post by wibel)
I do understand it and I sketched the diagram but i don't see how they got the answer. (Answer: 2.0 m/s at 90 degrees to the bank)
Hi there, look at my above post again. It should be a bit more clearer hopefully.
17. Owww i understand it now, because it says his overall velocity is 2.3 m/s (which is the resultant) so we want the velocity perpendicular to the bank and therefore we use pythagoras to get the smaller side - that's right isn't it?
18. (Original post by wibel)
Owww i understand it now, because it says his overall velocity is 2.3 m/s (which is the resultant) so we want the velocity perpendicular to the bank and therefore we use pythagoras to get the smaller side - that's right isn't it?
Yup.
19. Cheers
20. Could anyone tell me if there is any difference between 'instantaneous speed' and 'instantaneous velocity', if yes what is the difference and if not then why not? please explain thank you

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