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14

On the whole, static friction is higher than dynamic friction. This means that if you can brake without your wheels skidding, you will come to a halt more quickly. So let's assume that the truck brakes without skidding, and see where that gets us. Let's assume that your truck has weight $W = Mg$ with a haystack with additional weight $w = mg$ on top. ...


14

Not to detract from Floris' answer, but I think this is an instance where it is nice to think in terms of limits. If the hay is tied down, you're stopping an object with mass (truck + hay). If the hay isn't tied down, but on a sufficiently sticky surface such that it doesn't move, it should be the same as stopping it if it were fixed, since the outcome is ...


5

There are two parts to this question. Part 1: will the card slide?if I have a card at an angle, is there a limiting vertical force that will make it slide sideways? The force diagram looks something like this: This is a bit like the "climbing a sliding ladder" problem, in which case there is going to be a limiting force F - once you exceed that force, ...


5

When you inhale you create an area of low pressure immediately in front of your mouth, like the Venturi of a carburetor. You would be drawn toward the low pressure area as the incoming stream of air accelerates down your throat, maintaining the low pressure in front of your mouth. Until your lungs are full. When you turn 180 degrees and exhale, you reverse ...


4

Fundamentally, this is no different from computing the friction in a fluid (shear viscosity). The theory of viscosity goes back to Maxwell and Boltzmann, and microscopic calculations are possible for many fluids. Solid friction is more complicated, because the exact preparation of the surface obviously matters. First principles theories therefore concentrate ...


4

The essence of static friction is that it acts to prevent motion even in the presence of some outside force. The desk I'm sitting at while I type this is homemade and thus almost certainly not perfectly level. Yet the items on the desk are all fixed in place, not sliding down the slight slope. (OK, pencils tend to migrate by rolling, but..). It's the ...


3

This is the simplest analogy I could think of. Imagine a long narrow carpet sliding across a huge ice rink at 1kph. On the rear end of the carpet stands a very fat (200kg) man wearing roller skates. You want to bring him to a standstill. You could grab the man and dig your ice skates into the ice until he eventually stops. Alternatively, you could grab the ...


3

Looking very close at the surfaces that touch at friction, this is an illustration Both surfaces are rough. They have ticks, holes, gabs, pits, spikes, and edges on the microscopic level. The smoother, the lower the coefficient of friction $\mu$. This constant is thus to be considered as a combined "roughness" between these two surfaces. Intuitively and ...


2

...a truck in motion and it has stack of hay (lets suppose) on the back. Now if the truck comes to a sudden stop will it stop faster if the force exerted by the truck on hay had overcome the friction force (another wording: will it be faster if the hay slips forward) or will it stop faster if the hay remains constant. I tried to find a braking ...


2

Imagine a box on a horizontal surface. If you just push it down should there be a friction force? If yes to which direction? Now imagine a box on an inclined surface. Static friction balances the component of weight that is along the surface. If you apply more force normal to the surface, does that component change?


2

Yes, you are thinking about it correctly. No force is required to keep the puck in motion. This is an important idea in physics. It is actually a common misconception among physics students that a force is required to keep an object in motion, so it is good you do not have this misconception.


1

No body is perfectly rigid. If you want to consider friction as due to small bonding sites, then those sites do move (strain) under load (stress). So the premise that no work is done because the binding locations are fixed is incorrect.


1

What is meant by this is the force normal to the surface of contact between an object and what it is resting on. In most problems like this, this object boundary is taken to be flat. The question is slightly mischievous: it's asking you to be precise to test your understanding of friction: to make the statement precise, you need to say that if the normal ...


1

Just a small conceptual hint will do No problem. A hint: Set up Newton's law, $\sum F=ma$. You will see that the sum of all the three forces must equal... yes, what should it equal? I'm confused with the condition at which the block will start sliding What is the difference in the equation mentioned above for a point just after it started moving, ...


1

All the other forces except friction acting on the ball have their line of action pass through the center of mass. So, friction is the only force which can provide torque in the above example. Therefore, in order for the ball to roll, you need friction.


1

Yes. The manner of which two surfaces in contact interact is highly investigated by the Tribology community.In particular, the field exploring the mechanics of the interaction is called contact mechanics. Tackling problems of contact mechanics analytically/numerically is often done by solving the elasticity equations. By predicting quantitatively the forces ...



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