Physics - Mechanics (Section 4)

Give examles of Scalar Quantities

Time, Distance, temperature, mass, speed, length, energy

What is the difference between scalar and vector quantities?

Scalars have a magnitude only, whereas vectors have a magnitude and direction.

Give examples of vectors

Weight, force, momentum, displacement, velocity, acceleration

What is important to remember about inclined plane problems?

W > W1 W>W2, therefore in right angled triangles with W1/W2 and W, W must be the hypotenuse

What are free body diagrams

Diagrams showing all forces exerted on a single object

What is Newton’s first law

If there are not resultant forces acting on an object then it will either remian at rest, or travelling at a constant speed/velocity in a straight line.

How to calculate resultant forces?

Draw forces tip to tail, the resultant force is from the first arrow to the end of the last arrow (closed vector triangles are formed in object is in equilibrium).

What is a moment?

The force x the perpendicular distance from the pivot to the line of action of the force.

What is the principle of moments?

The sum of the clockwise moments = the sum of the anti-clockwise moments (CM=ACM)

What is the centre of mass?

The point in which you can consider all the weight (of the object) acts through, no matter the orientation.

How to find the mass of an object experimentally?

• Cut a piece of card into any shape'

• Hang the card from a point (with a string and plumbob attached)

• Mark a straight line along the string (repeat at least twice)

• The point of intersection is the centre of mass

What concept do engineers use to improve stability.

The centre of mass with the concept of moments:

• A low centre of mass increases stability as tilting creates a moment to tip the object back onto its base

• A low and wide base increases stability.

When does an object topple?

The object topples when the line of action of its weight (acting through the centre of mass) falls outside the the base of support