Mechanics 1 Chapter 5 :: �Forces & Friction

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In Year 1 any frictional forces were stated. In this chapter, we will be able to calculate the frictional force using the normal reaction force acting on the object.

“Determine the magnitude and direction of the resultant force.”

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1:: Resolving components

2:: Inclined Planes

5m

7 N

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We can use exactly the same principle to find the components of a force, and convert between vector and scalar form.

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8 kg

Draw a clear force diagram, obviously!

8 kg

HIGHLY RECOMMENDED Fro Tips:

1. Use dotted lines for components of a force, to distinguish from solid lines for full forces.
2. Make sure the direction of your components is clear in the diagram, to ensure you get the sign right in calculations.
3. Write the values of your components in the diagram (as above).

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Method 2: Using Triangle Law for vector addition.

Fropinion: Hell no.

We can avoid resolving components by drawing the force vectors in a chain, then finding the vector from the start to end point. The resultant vector (orange) geometrically represents the same of the vectors.

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Pearson Mechanics 1

Pages 88-90

🖉 For problems involving inclined planes, resolve forces parallel and perpendicular to the plane.

10kg

Recall that I recommended you do components of a force as labelled dotted arrows.

Indicate direction of acceleration with double arrow.

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This means “resolving forces in the indicated direction”.

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Pearson Mechanics 1

Pages 92-93

Scenario 1: A block is on a horizontal rough surface with no forces (other than gravity) acting on it.

Comment regarding friction:

No frictional force.

Scenario 2: A cable is attached to the block and a force applied. The block doesn’t move.

Comment regarding friction:

There must be a force left (i.e. friction, which acts parallel to the plane) to counteract the tension force acting right. Note that as the tension increases but the block doesn’t move, the frictional force increases.

Scenario 3: The tension is increased until the block starts to move.

Comment regarding friction:

The friction reaches a maximum. Therefore if the tension increases further, there will be an overall force right and therefore the block accelerates. The friction is in the opposite direction to motion.

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[Textbook] A particle of mass 5kg is pulled along a rough horizontal surface by a horizontal force of magnitude 20N. The coefficient of friction between the particle and the floor is 0.2. Calculate:

1. the magnitude of frictional force
2. the acceleration of the particle.

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Recall that friction acts in opposite direction to motion.

Edexcel M1(Old) May 2013 Q3

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Pearson Mechanics 1

Pages 97-98

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Additional question:

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