Work and Simple Machines

Why have we been studying forces and motion? We need to understand motion and forces before we can understand work and simple machines The study of work and simple machines builds on knowledge of motion and forces

HOW WE HAVE ACCOMPLISHED THE COURSE OBJECTIVES 1.We have learned how to identify and describe change in position. 2.We have learned how to calculate speed. 3.We have learned how to measure and graph changes in motion. 4.We have learned how to identify and describe changes in direction and speed. 5.We have learned how unbalanced forces cause changes in motion. 6.We will now learn how force is related to work. 7.How do simple machines make work easier?

COURSE OBJECTIVES Identify and describe changes in position Calculate speed, distance, and time Measure and Graph changes in motion Identify and describe changes in direction or speed Relate unbalanced forces to changes in motion Relate force to the ability to do Work Explain how simple machines make work easier

We have learned how to identify and describe change in position. What is a change in position? Motion All motion is identified and described as being relative to a reference point. By measuring the distance an object moves relative to a reference point. By measuring the time it takes to move a certain distance. By calculating the rate at which an object moves. Using distance and time measurements to calculate the speed of an object. How do you identify and describe motion?

We have learned how to calculate speed How do you calculate speed? By dividing distance by time. Use the DST Triangle.

We have learned how to measure and graph changes in motion How do you measure changes in motion? By measuring the distance an object moves relative to a reference point. By measuring the time it takes to move a certain distance. How do you graph changes in motion? Using Position vs. Time and Velocity vs. Time Graphs: Time is on the x-axis, Position or Velocity on the y- axis. The slope of the line represents speed (PvT) or acceleration (VvT).

We have learned how to identify and describe changes in direction and speed What is change in direction or speed? Acceleration A change in an object’s velocity (speed or direction) is acceleration (may be positive or negative)

We have learned how to identify and describe changes in direction and speed How do you identify and describe changes in direction? Position vs. Time and Velocity vs. Time Graphs: PvT – slope changes from positive to negative or negative to positive; VvT – y-axis value changes from positive to negative or negative to positive

We have learned how to identify and describe changes in direction and speed How do you identify and describe changes in speed? Position vs. Time and Velocity vs. Time Graphs: accelerating or decelerating; PvT – slope changes; VvT – y-axis value changes;

We have learned how unbalanced forces cause changes in motion What are changes in motion? By changing position, direction or speed of an object. Changes in the direction or speed of an object is acceleration, so unbalanced forces cause acceleration. Increase or decrease in speed, starting or stopping, changing directions How do unbalanced forces cause changes in motion?

We will now learn how force is related to work What is work? How is force related to work? The force and the motion of the object must be in the same direction There are three key ingredients to work - force, displacement, and cause. Work = F x D Work is using force to move an object over a distance. When a force acts upon an object to cause a displacement of the object, it is said that work was done upon the object.

How do simple machines make work easier? What is a simple machine? A mechanical device that makes work easier to perform. The simplest mechanisms that provide mechincal advantage What is mechanical advantage? A measure of the force amplification achieved by using a tool, mechanical device or machine system. When a machine takes a small input force and increases the magnitude of the output force, a mechanical advantage has been produced. Mechanical advantage is the ratio of output force divided by input force. If the output force is bigger than the input force, a machine has a mechanical advantage greater than one. MA = Force OUTPUT /Force INPUT How do simple machines make work easier? By changing the direction or magnitude of the force (enable a person to apply less force or to apply force in a direction that is easier to manipulate). By transferring a force from one place to another, changing the direction of a force, increasing the magnitude of a force, or increasing the distance or speed of a force.

How do simple machines make work easier? What is a simple machine? What is mechanical advantage? MA = Force OUTPUT /Force INPUT Mechanical advantage is the ratio of output force divided by input force. If the output force is bigger than the input force, a machine has a mechanical advantage greater than one. A mechanical device that makes work easier to perform by providing mechanical advantage

COURSE OBJECTIVES Identify and describe changes in position Calculate speed, distance, and time Measure and Graph changes in motion Identify and describe changes in direction or speed Relate unbalanced forces to changes in motion Relate force to the ability to do Work Explain how simple machines make work easier

HOW IS IT ALL CONNECTED? Motion is described relative to a reference point: when an object changes position, we can measure the distance travelled and the time it takes With distance and time measurements, we can calculate the speed of an object. Use the DST triangle to get distance, time, and speed We can use Position vs. Time graphs and Velocity vs. Time graphs to visualize changes in an object's position or velocity The slope of a line in a Position vs. Time or Velocity vs. Time graph shows changes in the object's speed or acceleration Unbalanced forces cause changes in acceleration: in order for an object's motion to change, the forces acting on it must be unbalanced Unbalanced forces are required to do work on an object; work is force applied over a distance A simple machine makes work easier to perform by changing the magnitude or direction of the force. It provides a mechanical advantage