PHYSICS: Mechanical Equilibrium What usually comes to mind then you hear the phrase: “mechanical equilibrium”? Imperial Walkers? Mechanical, but probably not…

PHYSICS: Mechanical Equilibrium What usually comes to mind then you hear the phrase: “mechanical equilibrium”? Whiney Jedi? Again, probably not…

PHYSICS: Mechanical Equilibrium What usually comes to mind then you hear the phrase: “mechanical equilibrium”? Asthmatic super- villains? Awesome movie effect, but no…

PHYSICS: Mechanical Equilibrium What usually comes to mind then you hear the phrase: “mechanical equilibrium”? Duh, silly… FORCE!

QUESTIONS AND ANSWERS WITH EINSTEIN Q: What is a force? A: A force is any external push or pull exerted on an object.

QUESTIONS AND ANSWERS WITH EINSTEIN Q: What forces are acting on the book in the picture below? A: Weight and Normal normal force weight

FORCES FORCE –any external push or pull exerted on an object WEIGHT –the effect of gravity acting on the mass of an object Weight could also be thought of as the force of gravity NORMAL – the force of a surface pushing back on an object A normal force is also known as a supportive force. A normal force is always PERPENDICULAR to the surface.

FORCES PHYSICS According to GABE What is a force? For some reason, I always thought that force was a power that balanced out good and evil in the universe.

FORCES PHYSICS According to GABE What is a force? Luke…use the force. May the force be with you… I guess I gotta quit watching so much T.V.

FORCES NET FORCE –the combination of all forces acting on an object Since force is a vector quantity, the direction of the forces must be considered when figuring the net force. EQUILIBRIUM –the fancy name for when the net force equals zero Static Equilibrium occurs when an object is at rest. Dynamic Equilibrium occurs when an object is moving at a constant velocity.

QUESTIONS AND ANSWERS WITH EINSTEIN Q: What type of motion is occurring when the net force equals zero? A: Zero net force means that an object is at rest. Thus, there is no motion. A: Zero net force could also mean than an object is moving at a constant speed. OR…

FORCES NET FORCE –the combination of all forces acting on an object Since force is a vector quantity, the direction of the forces must be considered when figuring the net force. EQUILIBRIUM –the fancy name for when the net force equals zero FREE-BODY DIAGRAM – a sketch used is to illustrate the forces acting on an object Free-body diagrams use arrows to indicate the magnitudes and directions of the forces.

QUESTIONS AND ANSWERS WITH EINSTEIN Q: What forces are acting on the book in the picture below? A: Weight, Normal, and Friction normal force weight friction

QUESTIONS AND ANSWERS WITH EINSTEIN Q: Is there motion in this situation? Is there a net force? A: No motion implies that the net force equals zero. normal force weight friction

FORMULAS FOR-m-U-las Mathematical Version of Net Force If an object is in a state of mechanical equilibrium then the net force on the object is zero: NOTE: The “sigma” (  ) notation means that you need to “sum up” the forces.

FORCES Forces are vector quantities. This means that: EXAMPLE: Find the net force on the box. Assume it stays on the ground. 1) The direction is important (FBD helps here). 2) The magnitude may have components in two dimensional situation (FBD helps here too). 3) Different forces acting on the same object can be combined in differently to yield the net force. 20 N 10 N 30 N

FORCES EXAMPLE: Find the net force on the box. Assume it stays on the ground. 20 N 10 N Forces are vector quantities. This means that: 1) The direction is important (FBD helps here). 2) The magnitude may have components in two dimensional situation (FBD helps here too). 3) Different forces acting on the same object can be combined in differently to yield the net force.

FORCES EXAMPLE: Find the net force on the box. Assume it stays on the ground. 10 N 0 N Forces are vector quantities. This means that: 1) The direction is important (FBD helps here). 2) The magnitude may have components in two dimensional situation (FDB helps here too). 3) Different forces acting on the same object can be combined in differently to yield the net force.

FORCES EXAMPLE: Find the net force on the box. Assume it stays on the ground. 20 N 30° 17.3 N Forces are vector quantities. This means that: 1) The direction is important (FBD helps here). 2) The magnitude may have components in two dimensional situation (FDB helps here too). 3) Different forces acting on the same object can be combined in differently to yield the net force.

FORCES EXAMPLE: Find the net force on the box. Assume it stays on the ground. 20 N 30° 27.3 N 10 N Forces are vector quantities. This means that: 1) The direction is important (FBD helps here). 2) The magnitude may have components in two dimensional situation (FDB helps here too). 3) Different forces acting on the same object can be combined in differently to yield the net force.

PHYSICS IS PHUN!