The resistance a surface or object encounters when moving over another.

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Showing that a mass moves a half cycle

Consider a mass $m$ at position $x(t)$ on a rough horizontal table attached to the origin by a spring with constant $k$ (restoring force $-kx$) and with a dry friction force $f$ $$\begin{cases} ...
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2answers
25 views

Velocity and acceleration with variable friction

If you have a body on a table,with a velocity $u_0$, going from a non friction area to a friction area, how do I find the function for velocity and acceleration due to the variable friction force(T). ...
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0answers
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A problem from the Rudolf Ortvay Competition in Physics [on hold]

PROBLEM STATEMENT: A uniform circular disc is kept face down on a table which has a uniform friction coefficient.It is pushed in such a way that there is translational as well as rotational motion of ...
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1answer
30 views

Question based on friction force [on hold]

How will you solve this question using high school physics? It is based on friction force (as you can see, obviously). I have problem determining the direction of friction.
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1answer
30 views

What is force of static and kinetic friction? [on hold]

While I am asking more than one question in this thread they are all small concept tests that you can answer with a yes or no, and is all related to me understanding kinetic and static friction. ...
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3answers
58 views

A block sliding down a ramp lab (with friction), I keep getting a higher final energy than initial

A block of 55 g is sliding down a ramp of 35 degrees of inclination. The hypotenuse of the ramp is 63 cm and the height is 36 cm. vi = 0 as the block starts at rest. I did 3 trials of letting the ...
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6answers
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Why is friction force negative in ice skater problem?

A 68.5 kg skater moving initially at 2.40m/s on rough horizontal ice comes to rest uniformly in 3.52s due to friction from the ice. What force does friction exert on the skater? I am not really ...
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0answers
38 views

Inclined plane problem - admission exam [closed]

This following problem was featured on my Physics admission exam and I didn't know how to approach it properly : Consider an inclined plane at an angle $\theta = 45 ° $ of mass $M = 9 kg$. On the ...
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1answer
18 views

How is inertia related to friction?

Inertia is the tendency for moving object to continue to move at constant velocity. My book says "in order to initiate motion in an object, inertia must be overcome to start the movement." But that ...
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1answer
48 views

Work done by friction on a ball flying through air [closed]

A baseball of mass 145 g leaves a pitcher’s hand at 150km/hr, but due to constant air resistance, it arrives at home plate 20.0m away traveling at 145km/hr Assume that the magnitude of the ball’s ...
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0answers
36 views

Physics Question [closed]

A horizontal spring with spring constant 150 N/m is compressed 18cm and used to launch a 2.9kg box across a frictionless, horizontal surface. After the box travels some distance, the surface ...
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1answer
25 views

Does a propeller being pushed through the air have more friction if free to spin?

I just passed a boat being pulled on a trailer and noticed the propeller spinning in the wind. I began considering the possibility that a propeller free to spin might cause less friction against the ...
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3answers
58 views

How to apply Newton's first law to moving object?

I'm new to many forces, such as gravity and friction, and I don't really know how they work. I'm trying to simulate a ball bouncing with a program, and it travels at a constant speed horizontally. I ...
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2answers
74 views

A confusion regarding friction

Suppose there is a block which is being pulled by two forces A,B in opposite direction(as shown in figure). If we have no information regarding the forces $A$ and $B$, can we tell whether there is any ...
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14answers
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Is it possible to walk in a friction-less world?

Is it possible to walk in a frictionless world. I think you won't be able to walk because walking depends on friction acting on your feet. I think about it like an ice rink because when you try to ...
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1answer
50 views

How does a skater moves by pushing sideways?

Take a look at this video http://www.youtube.com/watch?v=EmMf91AVUXc or take a look at the following screenshot. As you can see, the skater pushes almost perpendicular to the direction of movement ...
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2answers
728 views

Does body weight affect the speed when going downhill on a mountain bike?

We know heavier objects fall faster when dropped at certain height. I was wondering if I am going downhill on my mountain bike without any peddling, will I travel faster or slower because I am fat?
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1answer
43 views

Friction as a Non-conservative force

Intuitively, one can find friction to be a non-conservative force. How can one prove that it is non-conservative?
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3answers
42 views

Frictional forces apposing motion

Please could someone help with some physics about resistive forces that would slow a ball down which is rolling across a floor. I have found conflicting bits of information about the effect friction ...
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0answers
28 views

Why is $f_\mu=-\mu |<w, -v>|\tau$

Given a point-like object $M$ with weight $w$ traveling down a curve $\gamma$ with constant gravity experiencing a frictional force $f_\mu$. Let $v$ denote the unit normal vector to $\gamma$ at $M$. ...
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2answers
36 views

Does rolling friction depend on area of contact?

We know that forces of static or kinetic friction do not depend upon the area of contact of the two surfaces, is it applicable to rolling friction as well?
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4answers
924 views

Does stopping the same bike and rider at the same velocity with the front brake require less energy than the back brake?

It's the same body made by the rider and the bike moving at the same speed. So, even though braking on the front/back alters the normal forces on the opposite wheels thus creating more friction with ...
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1answer
34 views

Are coefficients of friction invariant by switching the materials?

I don't have the ability to make the experiment to answer these questions : Let $A$ and $B$ be two materials. Is the static coefficient of friction of $A$ on $B$ equal to the static coefficient of ...
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1answer
34 views

Work done by friction on a body?

I know that when a body slides over a surface, the work done by friction is not stored as potential energy in the body. It is dissipated in the form of heat. But why is it not stored as potential ...
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2answers
41 views

Why is sliding friction more than rolling friction? [duplicate]

Frictional force doesn't depend on area of contact. So why is co efficient of rolling friction less than coefficient of sliding friction?
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0answers
25 views

Flow Rate Calculation from a drain tank through a pipe [duplicate]

I want to know how to calculate the flowrate (Q) of a drain tank flowing through a pipe (see the figure below) All I know is that Q=Velocity(V) x Area (A) V= sqrt(2*g*H)=sqrt(2*9.81*10)=14m/s. I ...
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2answers
170 views

Conceptual rolling

If you could roll a ball down a slope with friction, we would all know which direction the ball is rolling. However, say we have a frictionless slope and we roll the ball in the opposite direction and ...
2
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1answer
56 views

Damping a spring force

I'm modelling particles in a system using a spring and damper force. $$F= kx -cv$$ $x=x_i -x_f$, where $x_i$=centre of spring and $x_f$= displaced position. Above $x$ is the displacement and $v$ is ...
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2answers
126 views

What would happen if there was no friction on earth? [closed]

I'm not talking about zero-g or a vacuum. If oxygen, gravity, air pressure, etc still existed but if there was suddenly no friction, anywhere.
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5answers
174 views

Why does solving $\mu mg = m \frac{v^2}{r}$ give the *max* possible velocity?

So here is the standard problem setup of a car turning on an unbanked road: A 1000 kg car is going around a curve with radius 30 meters. If the coefficient of friction between the car's tires ...
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1answer
26 views

About friction contributing to speed

Friction in our daily experience is understood as a resisting parameter to the effort putted for moving an object on a surface. I understand friction as a negative force by describing what happens to ...
2
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2answers
75 views

Can negative friction exist? If so, what happens?

I have to talk about negative friction for my oral exam and I would like you to comment my presentation. I know that friction is the resistance to motion that occurs between objects. So friction is ...
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1answer
31 views

How much energy is saved when using luggage with wheels? [closed]

How much energy is saved when using luggage with wheels as opposed to carrying the luggage? Thanks.
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2answers
51 views

Friction in Rolling Motion [duplicate]

My understanding of rolling motion: When a body rolls, at every instant, there is just one point of contact between the body and the plane and this point has no motion relative to the plane. Now ...
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1answer
29 views

Darcy friction factor

I have an assingment that says: How is the friction factor $f$ dependent of the roughness $\epsilon$ and Reynolds number $Re$? The equaton for the friction factor is ...
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1answer
37 views

What is the best way to calculate speeds at other points in a venturi-tube when knowing one?

I and a friend have made a venturi tube trough which water flows at a low speed. The flow is therefore laminar. We measured the static pressure using some piëzometers at the points 1,2 and 3. We know ...
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0answers
41 views

How to locate the initial speed? [closed]

I have this question: Two men were delivering a crate of mass $100~\text{kg}$ to a house up a hill which is inclined at $35^\circ$, when it dropped and slid down the hill. The coefficient of ...
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2answers
43 views

In what form is the energy stored in this situation?

Consider a hypothetical situation, A person is pushing a block of some arbitrary mass in vacuum (no external forces are involved) and due to this, if I am not mistaken, the person is doing work and ...
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2answers
25 views

Get coefficient of friction given mass, forward force, and acceleration?

I'm aware that this is extremely basic but I've forgotten how to get the coefficient of friction when given a forward force and acceleration. Can someone describe to me the algorithm for solving the ...
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1answer
36 views

How to calculate friction on a spinning ball on the ground?

If there is a ball on the ground initially at rest, Assume that the plane xoy(cartesian) is the ground and that Z is the normal of the ground. If I spin the ball so that $\omega_x=\omega_y=0$ and ...
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1answer
48 views

General solution of a mass spring system

This is the differential equation that describes small amplitude vertical oscillations of a mass $m$ that is hanging from a spring $$\frac{d^2x}{d t^{2}} + \frac{b}{m}\frac{dx}{dt} + \frac{k}{m} x = ...
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2answers
45 views

confused about the direction of friction force

I'm really confused about the direction of friction force. I think about collision of two balls and think that "friction force is opposite to the relative speed of the contact point of the two ...
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2answers
32 views

direction of friction on an object rolling with constant speed

Although there are many questions similar to this, but none of these specifically talk about the situation with constant speed. A wheel is rolling on a horizontal plane (having some friction) ...
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0answers
33 views

Paradoxical Friction When Frying Eggs

I cook scrambled eggs for breakfast in an 8-inch diameter non-stick frying pan with sloping sides (approx 45 degrees). I cook the eggs in a lot of butter and bacon grease that is melted firest, so ...
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3answers
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Paradox in the two block problem [closed]

UPDATE (regarding duplicate) : This question is not a duplicate of another question. Sure, the situation in both the questions is same and, yes, both questions ultimately provide a methodology to ...
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1answer
42 views

If I shoot a hockey puck on ice, is the force of me shooting it applied throughout its travel, or is it a one time force?

For example, if I take a slap shot on a hockey puck, from what I understand, the forces acting on the puck are friction, the normal force, and the puck's weight. And, since I'm not constantly either ...
1
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1answer
56 views

On the work done by friction

The work done by friction is often calculated just as we would with any force. If we give a block of mass $m$ a velocity $v$ on a rough surface and it comes to rest after traversing a distance $x$, ...
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0answers
30 views

Force acting on a wheel of a two-wheeled self balancing bot

Proceeding further with my work on a self-balancing bot as posted here: http://bit.ly/1FfI6LK I've gotten stuck at the following equation: n = Gear ratio $K_t$ = DC motor torque constant $i_l$ = DC ...
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1answer
29 views

How to mute Sliding Friction

I solve rubik's cubes and do it a lot. However, a lot of people around me get annoyed when I do it because it gets really scratchy when I go fast. I know this is because of the sliding friction ...
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1answer
29 views

Condition for sliding of two blocks placed one over another and connected by spring

A constant force F is applied to smaller mass till M slides. The spring constant is k. Now it is asked to find k. I'm confused with the condition at which the block will start sliding. Can ...