Chapter 1.1

Force In Mechanical Systems

What Are Mechanical Systems?

• Basically the “simple machines” that you learned in Elementary school– Levers– Gears– Pulleys– Ropes & Chains

Measurement

• Metric System – aka SI System– Base Units• Meter• Kilogram• Second• Ampere• Kelvin• Mole• Candela

• English System – U.S.A. only– Base Units• Foot• Slug• Second• Ampere• Fahrenheit• Mole• Candela

Mass vs. Weight

• Mass– The amount of “stuff” an

object has inside of it– Does not change

regardless of where you are in the Universe

• Weight– The force exerted on the

mass inside an object by another larger body.

– Weight does not noticeably change according to your position on the Earth

– Weight does change depending on your position in the Universe

Describing Force

• When we describe a force we always give its Magnitude and Direction

• We call these Vector quantities• We can diagram forces using arrows• The direction of the arrow describes the

direction of the force while the length of the arrow describes its magnitude.

Balanced vs. Unbalanced Forces

• Balanced Forces– While you are sitting in

your chair, your weight is pushing down on the chair and the chair is pushing back with the same force – you do not move.

– We say that there is a Net Force equal to 0 or that the system is in Equilibrium

• Unbalanced Forces– When you press the

accelerator pedal to move your vehicle, the engine exerts a force through the transmission, gears and tires to overcome the forces of gravity and friction to cause the car to move.

– If we add up all the forces, it would not equal 0 and we would have an unbalanced system causing a change in motion.

Balanced Does Not Mean Stationary• An object can have a net force of 0 and still be moving.– Consider a satellite orbiting the Earth – Is it stationary?– Is it accelerating or decelerating?– Is it changing direction and falling to Earth?

• It is in a constant orbit moving at the same speed and direction basically forever unless something hits it causing it to change its motion.