Mechanical Equilibrium

Force – a push or a pull

Equilibrium – equality on 2 sides of something

Thermal Equilibrium – a thermometer acquires the same temperature as what it is measuring

Mechanical Equilibrium – the object is stable, there are no changes in its motion

A force is needed to change an objects motion

Net Force

Most often, more than 1 force acts on an object at the same time.

Net Force is the combination of all forces acting on an object.

Tension – stretching force (springs, rubber bands, etc.)

Weight – force of gravity pulling on the mass of an object

Vector – an arrow that represents the magnitude and direction of a quantity

Vector Quantity – needs both magnitude and direction for a complete description

Force is a vector quantity

Scalar Quantity – can be described by magnitude only, has no direction

Time, area and volume are scalar quantities

Exercises Worksheet: 2.1 Force

Mechanical Equilibrium – no physical changes occur; it is a state of steadiness

Equilibrium Rule – When a net force is 0, the object is in mechanical equilibrium

Σ F = 0

(the sum of all of the forces is equal to zero)

Support Force

Support force is the upward force that acts opposite the force of gravity.

Support force is often called normal force.

For an object to be at rest, the magnitude of the support force has to be equal to the magnitude of the object’s weight. The direction of the 2 forces will be opposite.

Bathroom Scale

The mechanism of the scale is calibrated to measure the support force in the compressed spring.

This support force is equal to the person’s weight.

The state of rest (not moving ) is only one form of equilibrium.

Equilibrium is the absence of a change in motion – so, an object moving at a constant speed and not changing direction is also in equilibrium.

A hockey puck sliding in a straight line at a constant speed along the ice is in equilibrium.

Static Equilibrium – objects that are at rest.

Dynamic Equilibrium – objects moving at a constant speed and in a consistent direction.

Bad Physics Pick-up Line:

I was only scalar until you came along and gave me direction.

The person suspended by the rope has a weight of 300 N.

The tension on the scale, therefore, reads 300 N.

If the person is hanging by one rope, then it is going to have tension equal to the person’s weight.

But, if the person is hanging by 2 ropes, the tension is divided between the 2 ropes, and so on.

Combining Vectors

For Parallel Vectors:

If they are in the same direction, they add.

If they are in opposite directions, they subtract.

The sum of two or more vectors is called their resultant.

Combining Vectors

For Non-Parallel Vectors:

Parallelogram Rule – construct a parallelogram so that the 2 vectors are adjacent sides.

The vectors are perpendicular.

The two vectors make adjacent sides.

The resultant is the vector at the center of the point where the two vectors meet.

Non-parallel and non perpendicular vectors

Assignment