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by Ron Kurtus

A total of 162 comments and questions have been sent in. They are listed according to date.

## List of most recent 10 letters

### Country

Force Affects Motion Will different surfaces affect speed? Jordan

Centrifugal Force Do forces cancel out? UK

General Confused about the definition of work Pakistan

Characteristics of Force Three characteristics of a force Uganda

Force Between Two Objects Kg are units of mass and not weight UK

Characteristics of Force What is pressure? India

Force and Motion Force acting on an object at an angle India

Characteristics of Force Is pressure found in force? Nigeria

Characteristics of Force Why is friction less than pushing force? India

Characteristics of Force What is the advantage of a maglev train? India

Next 10

## Will different surfaces affect speed?

Topic: Force Affects Motion

### Question

February 21, 2016

will different surfaces affect a speed of an object??

leen - Jordan

26798

If an object is sliding along a surface, the amount of friction between the two surfaces will affect the speed. A rough surface will usually have more friction resistance than a smooth surface and thus slow down the speed of the object more.

## Do forces cancel out?

Topic: Centrifugal Force

### Question

December 24, 2015

"A centrifugal force is the outward inertial force on an object moving along a curved path. An object will move in a curved path provided some force is preventing it from moving in a straight line, which is the centripetal force."

The above is incorrect. A rotating object "Exerts" a centripetal force, it is not subject to such a force. If a rotating object is acted upon by both a centripetal and a centrifugal force, which is what you are saying, these forces would cancel out.

Frank - UK

26648

If an object is held to a rotating disk by friction or some other force, it will experience a centrifugal force that seems to pull it outward.

The friction or other force--such as a rope attached to the center of rotation--applies the centripetal force.

Once the friction is released, the object will fly outward in a straight line due to its inertia.

There is no such thing as a single force, according to Newton's Law of Action and Reaction. Thus the forces do not cancel out.

## Confused about the definition of work

Topic: General

### Question

August 26, 2015

I am confused about the mathematical form of work defination w=fd i think that it was wrong becase when we further elaburate it i.e w/d=f so from it we get that force is inversely proportional to displacement and e.g if we are applying force on a wall with our body then the wall will not cover any distance at that time but we are doing work on it and applying force on so why it was not covering any distance .

faraz - Pakistan

26339

When you push on a wall, it seems like you are doing work. However, the scientific definition of work requires motion. Work is the force on an object that is resisting motion times the distance it is moved.

For example, when you push on a heavy box, it is being held back by the force of friction. You are not doing any scientific work until you are able to move that box.

## Three characteristics of a force

Topic: Characteristics of Force

### Question

September 28, 2012

state the three characteristics of a force?

kityo - Uganda

22963

The magnitude of the force, its direction, and whether the force is active or reactive. A push is active, while something like friction is a reactive force.

## Kg are units of mass and not weight

Topic: Force Between Two Objects

### Question

June 13, 2012

For the boy/girl attraction you have converted their 75/50kg 'weights' into masses, only you already have the masses. kg is the unit of mass!

- UK

22717

It is common—-but scientifically incorrect—-to state a person’s weight in kg, which is mass. However, care must be taken to distinguish between units of weight and mass. Newtons or kg-force are weight and kg or kg-mass are units of mass.

I updated the page to clarify that the weights were in Newtons or kg-force.

## What is pressure?

Topic: Characteristics of Force

### Question

May 22, 2012

what is pressure?

sanjay - India

22670

Pressure is the applied force times the surface area.

## Force acting on an object at an angle

Topic: Force and Motion

### Question

March 25, 2012

Sir,
I just went through one of your articles - 'force affects motion'. I came to know, 'It is possible that the object
keeps going at the same speed, if the force is applied perpendicular to the direction of motion of the object. In this case only the direction and hence velocity changes (even if speed remains constant).'

But i have a question. Is there any case, when a force, (acting at an angle to the direction of motion of an object) changes its direction as well as speed? Is it possible that the force changes both i.e. magnitude of speed and direction of motion of the object? Plz do reply Sir. I'll wait for that. And i'm very thankful to you for that article. THANKS!!

Abhishek - India

22534

Yes, it is true that the speed of an object remains the same if the force on it is perpendicular to the direction of motion. But note that the force must be instantaneous, such as with a collision. If the force continues on the object, it will be pushing on the object in the direction of motion and thus increasing its speed.

If the force pushes on a moving object at an angle in the direction of motion, the force will change both the direction and speed of the object. You can break the direction of the force into vector components to see one component perpendicular to the motion of the object and one component in the same direction.

For an illustration, see Vectors in Gravity Equations

## Is pressure found in force?

Topic: Characteristics of Force

### Question

February 29, 2012

Is pressure found in force?

22460

Pressure is the measurement of force divided by the area that the force is applied. If you push on something with a certain force, the pressure is that force divided by the area of your hand.

## Why is friction less than pushing force?

Topic: Characteristics of Force

### Question

November 25, 2011

i want ask that why friction is less than pushing force

tejinder - India

22206

Friction is a force that holds back a pushing force. If you can't move the object, the friction is greater than the pushing force. Once the object starts to move, the friction is less than the pushing force. See: Resistive Force of Friction for more information.

## What is the advantage of a maglev train?

Topic: Characteristics of Force

### Question

November 25, 2011

what is the use of maglav train insted of other trains pleasee give me a reseon

tejinder - India

22205

A maglev train is held above the tracks by a magnetic force. This means that there is no friction from having the train wheels rolls along the railroad track.

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