Physics P hysics L earning by I nedpendent E xperiments. R eading, and S tudy Center of Mass, Torque, Equilibrium, and Mechanical Advantage Vocabulary, Examples, and Concept Questions

The point in a system of bodies or an extended body at which the mass of the system may be considered to be concentrated and at which external forces may be considered to be applied. Gravity acts on the person ’ s center of mass and the center of mass follows a parabola, just like a tossed ball would. Where is the center of mass of a person? Center of Mass

An object ’ s center of mass must be above its support, if it is resting on a surface or below its support if it is hanging. Gravity acts on the vehicles ’ center of mass. What happens when the two vehicles are on a slope? Which vehicle is more stable? Why? Stability

Dr. Hair visits a sculpture park How can this sculpture be stable? Where is its center of mass?

Torque Torque equals the product of perpendicular Force and the Distance of the Lever Arm Produces a change in rotation of an object, in the same way force produces a change in linear motion, or acceleration. What is the unit of torque in the SI system? What is the torque applied in this picture by hand A in foot-pounds? By hand B?

Lever Arm or Moment Arm The perpendicular distance from the axis of rotation to the line along which the force acts. How do you maximize the lever arm when using a wrench? What happens to the torque applied, when the lever arm is maximized?

Two Conditions for Equilibrium Balanced Forces Balanced Torques

Types of Equilibrium

Examples of 3 equilibrium types What happens when a force is applied to an object in stable equilibrium? neutral equilibrium? unstable equilibrium? What is a real-world example of each type of equilibrium?

Mechanical Advantage Factor by which force is multiplied by a device or machine. The same work is done, but less force is applied for a longer distance. All simple machines and many tools use mechanical advantage to multiply force. Once you know what mechanical advantage is, you will see it everywhere!

Two ways to calculate MA In this example, Force Out = weight of crate Force In = pull on rope In this example, Distance Out = distance crate is lifted Distance In = distance rope is pulled For this pulley, IMA = 2 He pulls with half the force it would take to lift the crate BUT pulls the rope for twice the distance the crate is raised. For machines that are 100% efficient, IMA = AMA

Examples of Mechanical Advantage Lever Inclined Plane Wheel and Axle

Questions about Mechanical Advantage What are the units of mechanical advantage? What are three things you have done today that make use of mechanical advantage? What would make a machine less than 100% efficient? Which is larger, AMA or IMA, for real machines?

To Learn More about Mechanical Advantage Read the material in your PLIERS packet. Look for on-line resources Try this on-line tutorial: