6.2 – Using Machines

Objectives Explain how machines make work easier. Calculate the mechanical advantage of a machine. Calculate the efficiency of a machine.

Machine A device that makes doing work easier Machines increase applied force and/or change direction of applied force to make work easier

Ramps Increasing distance reduces the amount of force needed to do the work Machines = work easier

Force & Distance The same amount of work can be done when Applying a small force over a long distance Or applying a large force over a shorter distance Because work equals force times distance

Forces Machines help move things that resist being moved Input force = forces applied TO machine Output force = forces applied BY machine

Energy Law of conservation of energy applies…. The amount of energy the machine transferred to the object cannot be greater than the amount of energy transferred to the machine Some energy is changed to heat due to friction An ideal machine with no friction would have the same input work and output work.

MA = output force divided by input force Mechanical Advantage (MA) is the number of times a machine multiplies the input force MA = output force divided by input force

Ideal Mechanical Advantage The MA of a machine without friction Calculated by dividing the input distance by the output distance

Efficiency Measure of how much of the work put into the machine is changed into useful output work by the machine

Lubricants can make machines more efficient by reducing friction Efficiency = MA x 100% The efficiency of a machine is always less than 100% WHY? Because some energy is converted to heat due to friction Lubricants can make machines more efficient by reducing friction

6.2 Enrichment Tips Figure 3 will have 2 graphs (or 2 shaded areas, use different colors) Use IMA to figure out input force, take output force and divide by IMA Example: IMA of 3, output force 30 N Input force = 10 N

In-Class Assignment/Homework 6.2 Reinforcement & Enrichment WKT ORIGINAL EXTENSION #1 6.1c WKT -Force to Work to Power Problems p. 881 #63-64, 69