Find Force Req'd to Move Object: Weight & Calc Mu=F/Normal Reaction

[satishinamdar]

I want to know the fundamentals of finding the force reqd for moving a stationary object such as a car or a segway (which has got two wheels).
Also let me know in a formula mu = F/ NORMAL REACTION,
WHAT IS THE VALUE OF A WEIGHT HAS TO BE TAKEN?
meaning if weight of a person standing on a pedal of a bicycle is 40 kg then should I multiply with 9.81 ? or should I use figure of 40 alone?

 

[Bloodthunder]

Mass = in kg.
Weight = mass x gravitational acceleration, in Newtons.

 

[satishinamdar]

when we say a weight of 50 kg is kept on a table, then is it 50 kg ? and force applied vertically down is 50x9.81 kgf?In earlier days this Newton unit was not there , it is confusing.pl help.

 

[Bloodthunder]

The layman's term for weight is mass in physics. Both of these are in kg.
Weight in physics is the attractive force on the object by our Earth (or whatever planet you are on). This is in Newtons.

Also, the Newton unit has been around for... ~300 years? :)

 

[BruceW]

Weight is mass times the acceleration due to gravity. The acceleration due to gravity is almost the same everywhere on the surface of the earth, which is why people say weight when they actually mean mass.

e.g. If a mass of 50kg is kept on a table, then the weight of that mass is roughly 500Newtons (which equals the force down on the table).
Saying that something has a weight of 50kg is technically wrong.

Also, the force required to accelerate the bike+person is simply the mass of the bike+person times the acceleration.

The reason you need to keep pedalling to keep the bike at constant speed is because of air resistance. Friction with the road does not act to slow the bike (as long as the wheels don't slip).