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28

If there is no friction, you can still move by conservation of momentum. Take some stuff with you that you don't need. Throw it away in the opposite of the direction you want to go!

16

I assume by zero friction you mean no roughness or deformity in the ground. Perfectly smooth. Even so there is a way to walk. As you plunge your foot into the ground you compress it a little based on the atomic theory of matter. This impression allows your foot to be slightly lower than adjacent atoms and can therefore push away from them. On ice this ...

15

Although friction is not one of the four basic forces of nature, it exists because those basic forces exist. Friction is the resistance to motion of two objects held against each other. Friction that allows us to walk depends on gravity to convert our mass to weight which holds our feet against the surface where static friction enables the soles of our ...

14

It's very common to get mixed up about signs. The only recommendation I can give is to establish a clear sign convention and stick carefully to it. To show what I mean let's consider your skater: I'm going to use the convention that positive is to the right and negative is to the left. remember that quantities like velocity and acceleration are vectors, ...

11

Shift the upper configuration to the left a short distance at equilibrium. Result: the left wheel goes a little up, the right goes a little down, the train tilts clockwise, the center of mass is to the right of the centerline between the wheels, and therefore the center of mass provides a restorative force to push the train back to the right. Shift the ...

6

Heavier objects do not fall faster per se. But for heavy objects the influence of the air resistance will be smaller, if they have a similar surface area compared to the light objects. The answer depends on the properties of your tyres and the road. But on an even road the air resistance will typically dominate once you reach a certain speed (the friction ...

5

You cannot walk at all if there is no horizontal component of the force of interaction between you and the ground; by this definition "no friction" is tantamount to "no ability to move horizontally". But to add to Hapa's ANswer: you can move by throwing stuff. How do you do this? Here's one way if you don't have a handy sack of hammers ready in your pocket ...

4

The purpose of the question, as I read it, is related to an ideal condition (perfectly smooth surface) and a man with regular feet/shoes. In this case, normal daily walking would not be possible, as the horizontal force that moves the person ahead is coming from the friction between the feet and the ground. F = k*N; F : Force (horizontal) k: friction ...

4

YES walking is possible in a frictionless world with appropriate limb movements. The idea is to twirl the arms and legs to cause propulsion by the Magnus effect. The technique has been developed in a British government ministry https://en.wikipedia.org/wiki/Ministry_of_Silly_Walks Named for its investigator Gustav Magnus, the Magnus effect causes an ...

3

The answer depends on whether the wheels skid. When you brake with just the rear wheel, it's quite possible to skid; if you apply the front brake, the increase in normal force on that wheel tends to prevent skidding (although in extreme cases it could make you fly over the handlebars). Applying the rear brakes hard enough to block the wheel would generate ...

2

If you would have a rigid wheel and surface rolling without slip, then you would have no have a line contact between the wheel and the surface parallel to the axis of the wheel, which has zero surface area. This would not yield no rolling friction forces. In the real world nothing is completely rigid and would deform due to stresses. These deformations will ...

2

You are correct that the ball is not moving with respect to the floor, so we don't have to worry about kinetic friction at this interface. But since the energy loss there is so low, other areas of energy loss become significant. Small sources of loss need to be investigated to understand the picture. As you say, air resistance might show up as a big part. ...

2

Can it be shown mathematically using principles of mechanics that it is not possible to walk in a friction-less world, or is it only by experiment? It all depends on your definition of walk. If you mean, slide along a horizontal surface thanks to friction, then by definition no, it is not possible. Your critical angle is zero, so the horizontal ...

2

Yes. You need ridges (about 2mm tall): _____|~~~~~|______|~~~~~|____ You can walk on that if your tread is the right shape friction or not. Boot tread will interlock with the ridges providing non-friction-based traction and so the ability to walk.

2

If there is no friction, then you can not rely on it providing traction. However, other forces must still exist, or you'd fall through the floor! So, there is simple artificial solution to being able to walk in frictionless world. All that is needed is sufficiently contoured surface, something like this kind of knobs covering the surface: #### #### ...

2

The net drag force on the surface of the propeller is a function of the relative velocity of the fluid against the propeller's surface. The simple model for drag force that can be (loosely) applied to the question regarding the propeller is $$F_d=C_dA\frac{1}{2}\rho v^2$$ where $v$ is the relative velocity, $A$ is the projected area normal to the ...

2

No and yes. At first, your assumption is not quite correct. In vacuum, all masses fall at the same speed. The reason is the that the mass cancels in the equations of motion: $ma=mg$ $a=\ddot{x}=g$ To be more precise: the inertial mass and the gravitational mass are the same. Therefore, they cancel. However, things change when you take air resistance into ...

2

When the skater is on the ice, friction stops him/her in 3.52 seconds as you said. The molecules in the skates rub against the molecules in the ice, and the ice molecules absorb some of the skate molecules's energy, slowing the skater down. The reason the force is negative is because the friction is acting in the opposite direction of the skater's motion. ...

1

It's all a matter of how you've chosen your coordinate system. Think of how the velocities were calculated. They essentially looked at two points in time and the two corresponding points in space. If your positive direction is to the right, and the guy has advanced to the right, then its a positive number for velocity. Force carries the same logic here. The ...

1

What everyone said, but also: the way the question is phrased, the model it uses, is a 1-dimensional model. Imagine a point travelling along the real number line/the x-axis on a cartesian plane. The model in the problem assumes there is no vertical movement, or 'side to side', but only 'pure' 1-D movement along a straight horizontal line. There is only that, ...

1

Other people have answered your questions about the signs; I want to address your comment, "why does this sound like the normal force?" By Newton's third law, pairs of forces always come in equal and opposite pairs. If the ground exerts an upward normal force on you, you exert a downward normal force on the ground. If sliding on the ground exerts a ...

1

Inertia is just another name for mass: it is the property that if you kick a rock so that it makes a certain arc, it will take twice the force to make that arc when you kick two rocks glued together (twice the mass, twice the inertia). You do not really "overcome it" in the sense of finally being victorious and never having to care about it again. In ...

1

You can rearrange the equation by dividing m: $$F = ma ⇔ a = \frac{F}{m}$$ Now, knowing the force of friction, you can calculate the acceleration. The last remaining step is to calculate the velocity. To do so, there are two possibilities you could choose: The exact solution. To gain it, you will have to solve something called a differential equation: ...

1

Suppose the friction is given by $f$. For the sake of convenience It is taken as constant. Suppose the ball of mass $m$ is given an initial force of $F$ infinitesimally greater than $f$ so that it starts moving initially with infinitesimal acceleration but as there is friction, the extra kinetic energy gets converted to heat energy while the ball works ...

1

The simplest way to model friction to solve your problem is through something called the coefficient of restitution, which gives the ratio of the ball's speed after and before the bounce. $$C = \frac{v_f}{v_i}$$ So everytime the ball hits the ground, you can use the coefficient of restitution to calculate the new velocity based on the previous velocity. ...

1

Some people have suggested throwing something out--that's not walking. However, a world being frictionless does not mean that it is perfectly flat. You can walk by exploiting this fact--if a foot is in a depression you can develop a horizontal force no greater than the sine of the angle of the walls of the depression times your weight. Note, furthermore, ...

1

A conservative force must satisfy the property that the total work done must be independent of the path traveled. In physics, work is defined as the force along a given path times the distance of this path so that, simply: $$\text{work} = \sum_\text{paths} F\cdot l_\text{path} = \sum_\text{paths} \text{force along path}\times \text{path distance}$$ ...

1

You would think that Rolling Friction (or just friction in general) would depend greatly on the area of contact with the surface (and to some extent this is true), I mean, using logic, you could expect to think that if there are is a board of nails and you scrape your hand along it, it would hurt more to scrape your hand across more nails rather than less of ...

1

you're still converting the same amount of energy to heat, correct? Yes. In other words, brakes made from the same material on the same wheel should experience equivalent wear if each one converts X Joules of kinetic energy to heat energy, no matter if they are applied on the front or back wheel? I don't know. Why do you expect that "wear" is ...

1

'Rolling friction' isn't actually a frictional force in the same sense as sliding friction. The term 'rolling friction' is a little misleading, and is better named 'rolling resistance'. When something rolls, e.g. a wheel on an axis, a lot of forces go into resisting the rolling. These forces can include the friction of the bearings, the momentum of the tire, ...

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