Rock make scissor obey law of lever.
Yeah, but you’re going to run through a lot of scissors if your methodology is to beat them to death with a rock. 
If you look at a pair of open scissors edge-on, you’ll see that the two blades are not entirely parallel. The points should cross (visually), as if it would be impossible to close them because the points would collide. What happens as you close them is that the point of contact between the two blades remains under mutual pressure, with the blades sliding against each other. But even with that effect in action, they do their best cutting up close to the hinge. The hinge keeps the two blades tightly together so they slice through the material. As you progress outward to the pointy tips, you’re increasingly dependent on that slight bend and it can only partially compensate for the increasing distance from the hinge. Cheaper scissors (or older worn-out ones) may have an air gap between the two blades when they pass each other at the tip, and the material may not cut at all – it may wad up or even get pulled in between the two blades, intact, instead of slicing.
Excellent analysis! 
How are the mechanics of tin snips different from scissors? With scissors you get better cutting action with paper nearest the fulcrum. With tin snips however (at least the ones I’ve experienced) if you try to cut a piece of sheet metal like you would a piece of paper, opening the jaws as wide as possible and getting the metal as close to the fulcrum as possible, you just mangle the metal as it bends and mashes around. However if you nip at it with the tips of the snips then it cuts through with a satisfying snap. You don’t cut it so much as nibble away at it.
If it’ll help to clarify things, we can bolt one part of the scissors to the earth so that it doesn’t move, but this doesn’t change anything about the analysis. It also doesn’t matter whether the the user and the workpiece are on opposite sides of the fulcrum, or both on the same side of the fulcrum (like this cute pair of scissors). You can even combine those two concepts, i.e. a pair of scissors that’s bolted to the earth and has the user and workpiece on the same side of the fulcrum, like this paper cutter. The analysis of forces and motions doesn’t change: user applies force F1 at speed V1 at a distance D1 from the fulcrum, and at distance D2 from the fulcrum the lever exerts a force F2 at a speed V2, with the force ratio and speed ratio dependent only on the distances D1 and D2 from the fulcrum at which forces F1 and F2 are being applied:
F2 = F1 * D1/D2
V2 = V1 * D2/D1
A “standard lever” multiplies force and speed, and that’s it. What the user does with that force is an entirely separate issue, and doesn’t change the analysis of forces and motions. It doesn’t matter whether the applied force is used for shearing (scissors), pressing machine parts together/apart, moving a boulder, or whatever.
So far we’ve been discussing theoretical issues; you’re describing a practical aspect of scissors, and when you’re cutting stubborn material, it probably matters as much as being able to generate high cutting force. Placing stubborn material close to the fulcrum simultaneously solves both problems: the user has best mechanical advantage, and the short bending length (measured from the fulcrum) also assures that the blades will maintain contact with each other and provide reliable shearing action, even under high cutting forces.
Since most people are right-handed, scissors are usually made for use in one’s right hand; even on cheap ones without nicely molded grips, the lever stacking sequence on the pivot pin is typically chosen so that when closing the scissors, the user’s hand forces tend to help assure the blades remain in contact during the cut. This matters more on cheap scissors than expensive ones, as the cheap ones often have loose pivots and little or no lateral curvature to the blades. I’m left-handed, and when I was in elementary school in the late 1970s, it used to frustrate me whenever the art teacher handed me a pair of “lefty” scissors; despite writing with my left hand, I always used scissors in my right hand, and these “lefty” scissors always worked like shit for me. I didn’t understand it at the time, but the lever stacking sequence on those lefty scissors was reversed: if I had used them in my left hand, they would have worked as well as a “normal” pair of scissors worked in my right hand.
Qualified guess. Sheet metal is much thicker than paper, and also more resistant to shear. Close to the fulcrum the force of the blade is angled forward so some of it pushes the sheet “out” of the snips, further from the hinge the force of the blade is closer to vertical, relative to the sheet and so it cuts more easily.
The same applies to regular scissors if you try to cut something like really thick cardboard, I think.
The issue is that the already-cut portions of the workpiece need to bend to clear the fulcrum, but since the two pieces on opposite sides of the cut need to bend in opposite directions, the bend can only happen in the already-cut area. When you try to jam your workpiece in close to the fulcrum, you are shortening the available distance for bending. This isn’t a problem with flimsy standard office paper, but anything more rigid - posterboard, cardboard, or sheet metal - will fight you, and will also take on a permanent bend, which is usually undesirable.
For cutting sheet metal, the Beverly shear makes life easier. The blades don’t continue all the way to the fulcrum, and the fulcrum is moved up and out of the plane of the workpiece. The result is that the already-cut parts of the workpiece hardly need flex at all anymore, and in fact there’s a lot of room available for making curved cuts. Here’s one in action. Not as cheap or portable as handheld snips, but if you do a lot of sheet metal work, it’s a good investment.
A clearer comparison might be an axe, with a heavy sharp head some distance from the grip. When you wield the axe to get the head moving, the lever effect applies - it’s going to take more strength to get a long axe moving through the air than a short axe. But an axe doesn’t cut like a pair of scissors, you’re not applying much force when it strikes the target, you’re just guiding it onto the target. It’s the momentum that you previously imparted to the axehead that makes it cut.
Couldn’t tell you why, but as I went through this in my head to type it in, the person getting hit was on the ground. But yes that, and your next post.
Cutting metal with a tin snips is differant than using a scissors on paper.
I think Machine Elf has the better explanation.
For cutting a sheet of paper, you don’t need mechanical advantage. It’s pretty weak. If you try to cut thicker more resistant material, close to the pivot point (the hinge or screw or whatever you call it) works better. The ultimate example is wire cutters or toenail snips where the lever force is extreme.
You do see the same with hedge clippers. When snipping thin twigs, you can cut anywhere along the clipper blades. For big thick branches, the closer to the pivot point the better. Sometimes momentum helps, but for pure leverage, the closer to the pivot point the better.
Scissors and tin snips work on the same principle - an edge coming down against and parallel to another edge shears the material. For metal, this works better the flatter the shear is, so the further form the pivot point near the outside of the snips- but notice the snips do seriously take advantage of leverage.
Also, the problem with lever principle and scissors is that the thumb and fingers can only get so far apart, so scissors can only open so wide. Longer scissor handles mean the blade opens less wide. But since cutting paper requires very little force, there are very long scissors with normal short handles available. The purpose of scissors is to provide a cutting edge (or, a pair), not to heavily exploit leverage.
I’m not sure if you were responding to me, but if you were, this is what I was replying to:
Tin snips are designed to push the sheet metal out of the way as you cut it. Since sheet metal is so stiff, if you tried to cut straight through it, the cut the snips makes wouldn’t be large enough for the snips to pass through it.
When you use a scissors, the side of the paper you’re not holding (typically) falls below the scissors and you can keep cutting. With tin snips, it pushes the metal up/down to make a space. Further, some of them are meant for curving to the left or the right.
Having said all that, if you don’t know this and haven’t had any practice it’s pretty easy to make a mess of it.
Find a tin knocker and watch them. They’ll cut through it just fine, no mangled mess.
BTW, IME, you can find a tin knocker by shaking hands with people. They’re the ones that’ll shake your hand with such a string grip you’ll wonder if they broke it.
Another example of scissors designed to use leverage are many kitchen scissors. The handle is often longer than the blades. Esp. if they are (properly) designed for bone cutting as well.
Tin snips will also often have compound levers: Instead of just one pivot point, you’ll effectively have one lever pushing against the input of a second lever.
This has mostly been answered, but not framed quite like this, and sometimes more answers framed differently helps explain: it’s because scissors don’t cut by building up momentum before impacting the paper.
It’s the difference between a chef’s knife and a cleaver. They’re both fairly large knives, but the chef’s knife doesn’t have to be particularly heavy, because what’s providing the cutting force is the person pushing on it. A cleaver on the other hand, has to gain enough momentum to slice through bone, so it’s heavy, and you take big old whacks with it.
This question has been well answered but can someone explain the physics of striking a ball with a cricket or baseball bat when the point of maximum impact is nowhere near the end.
How do you figure? The bat is:
A)largest at the end, therefore having more physical contact with the ball
B)Moving the fastest at the end so it has the most momentum.
C)Heaviest at the end, also contributing to it having the most momentum.
D)The circle/path it creates is the shallowest at the end…that is, the bat and the ball will stay in contact for the longest time when the ball hit the bat near the end, giving the bat more time to transfer it’s energy to the bat, it also gives the ball the best chance of going straight.
I’m not quite sure I understand the question. It could be that you and I aren’t on the same page about the term ‘maximum impact’.
Here, the batter isn’t acting as a fixed fulcrum. You should think of the bat as a freely moving & rotating object. To transfer the maximum amount of momentum from the bat to the ball, you want to hit near the center of mass of the bat. If you hit exactly at the center of mass, though, you won’t transfer any of the angular momentum, so I think the optimal point is a bit further out than the center of mass.
Generally, it is the center of percussion:
a) This is not true at all.
b) Correct, so why is the optimum strike point nearrer the fulcrum
c) Not true.
d) Again wrong - See (b)