So far, we have discussed forces where have only dealt with explicitly applied forces on objects, where the force is considered as a contact* force.
However, in reality the actual contact between the surfaces of the objects in question also applies a force - that of friction.
In simple terms, the force of friction is the force that opposes the relative motion of an object.
This friction is determined by the force being applied between the surfaces (often the weight and thus the normal force) and the nature of the surface themselves.
However, in reality the actual contact between the surfaces of the objects in question also applies a force - that of friction.
In simple terms, the force of friction is the force that opposes the relative motion of an object.
This friction is determined by the force being applied between the surfaces (often the weight and thus the normal force) and the nature of the surface themselves.
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Theory
In this video we examine the principles of what friction is, the types of friction, and the mathematical models were use to calculate fictional forces. |
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Some problems
- A boulder of mass 45 kg is pushed on a surface with a coefficient of sliding friction of 0.85. What force has to be applied to produce an acceleration of 0.20 m/s/s (380N)
- A horizontal force of 30 N is required to slide a 12 kg wooden crate across the floor at a constant velocity, what is the coefficient of kinetic friction between the crate and the floor? (0.255)
- A sled is travelling at 4.00 m/s along a horizontal stretch of snow. The coefficient of kinetic friction is μk = 0.0500. How far does the slide go before stopping? (16.3m)
Want further practice? Here is another worksheet involving force and friction.
* Traditionally forces have been divided into contact forces, where two objects are 'in contact' with each other, and non-contact forces - such as gravity, magnetism and electrical charges. However, there is no actual contact between any two surfaces.
This animation shows that in reality two surfaces repel each other due to the negative nature of the outer parts of the atom (the electrons) and its the irregularity of the surface that determines the amount of friction
However, due to the complexity, we still model forces as either contact or non-contact, for learners learners, until they understand the nature of atoms and charge.
This animation shows that in reality two surfaces repel each other due to the negative nature of the outer parts of the atom (the electrons) and its the irregularity of the surface that determines the amount of friction
However, due to the complexity, we still model forces as either contact or non-contact, for learners learners, until they understand the nature of atoms and charge.
