Mechanical Force Notes

_____________ is a push or a pull

Force is a push or a pull.

Effect of force depends on:

Effect of force depends on: 1. Magnitude (strength) 2. Direction of the force

Force is measured in:

Pounds English System Newtons SI (System International)

Force can be measured by spring balances or ____________.

Force can be measured by spring balances or scales

___________ forces – equal and opposite. __________ forces – one side stronger. Gives a NET FORCE.

Balanced forces – equal and opposite. Unbalanced forces – one side stronger. Gives a NET FORCE.

___________ - shows only magnitude (strength) Examples:

Scalars - shows only magnitude (strength) Examples: Temperature, Elapsed time, pressure and mass.

__________ - shows both magnitude and direction. Examples:

Vectors - shows both magnitude and direction. Examples: Force, displacement, velocity, acceleration and momentum.

Vectors have magnitude and direction

Vector lines are drawn with an arrow. ___________ = magnitude of vector (strength) ___________ = direction the force is acting.

Vector lines are drawn with an arrow. Length of arrow = magnitude of vector (strength) Direction of arrow = direction the force is acting.

2 or more forces in the same direction – you can add to get the total force (net force). 2 or more forces in the opposite direction, you subtract to get the net force.

If forces don’t act along the same line – you cannot add or subtract If forces don’t act along the same line – you cannot add or subtract. You have to graph and measure the resulting line (or use trigonometry). You have 30 lbs pulling North and 40 lbs pulling East. What is the resulting force?

1. Chose a scale (say 1 cm – 10 lbs) 2. Graph the 2 forces at the correct angle matching the head of one line to the tail of the other line. 3. Draw the resultant line. Measure that line and use your scale to determine its magnitude.

_________ is force in rotation mechanical systems. It is measured in ___________ or __________ T=F x L

Torque is force in rotation mechanical systems. Measured in lb ft or N m T = F x L

Torque = _____________ x _____________ ____________ is the shortest distance from the rotation axis to the line of action.

Torque = applied force x lever arm The lever arm is the shortest distance from the rotation axis to the line of action.

If the lever arm is 12 inches (1 foot) and you use 40 lbs of force to turn it – find the torque:

T = F x L 40 lbs x 1 ft = 40 lb ft

You need 80 Nm of torque to turn a bolt You need 80 Nm of torque to turn a bolt. You can apply 100 Newtons of force. How long of a wrench (lever arm) do you need?

T = F x L 80 = 100 x L 80/100 = .8m T = .8 m