(7) Force, motion, and energy (7)  Force, motion, and energy. The student knows that there is a relationship among force, motion, and energy. The student is expected to: (A)  contrast situations where work is done with different amounts of force to situations where no work is done such as moving a box with a ramp and without a ramp, or standing still;

Work Notes Work - when a force (F) causes an object to move a distance (d) in the same direction of the force. Work = Force x distance W=F∙d

Direction of the motion Facts About Work: An object must move for work to occur. 2. That motion must be in the same direction as the force that was applied. Direction of the force Direction of the motion

Types of Measurements We have two general types of measurement: Quantitative measurements Quantity = Numbers Collecting numerical data Used more in physics than in biology Ex. “The apple weighs 25 grams.” (25 grams is the quantity) In science, we must always relate a number with a unit ex. 25 grams Qualitative measurements A description based on some characteristic of what is being measured. Not a number value but an observation that describes Ex. “The apple is red and round in shape.” (“red” and “round” are descriptors)

How is work Measured? (unit) Work formula: W=F·d Force (F) is measured in Newtons (N) Newtons are measured with a spring scale Distance (d) is measured in meters (m) We must convert all distances to meters Work (W) is measured in Newton meters (Nm) ↓ Work = Force x distance W=Fd W=Nm

Simple machines do not change the amount of work done Simple machines make work “easier” They do this by increasing the distance of the work, which decreases the force needed to do the work. W =↓F x d↑ 1. Work stays the same 2. Distance Increases ↑ 3. Force Decreases ↓

A boy gets angry and punches a wall with a force of 20N A boy gets angry and punches a wall with a force of 20N. The wall does not move. His mother carries a stuffed animal to him using a 3N force and walking a distance of 5 meters. Who did more work? Boy W=F∙d W=20N∙0m W=0Nm W=0 Jules Mom W=F∙d W=3N∙5m W=15Nm W=15 Jules

A girl wants to throw away a rotten apple A girl wants to throw away a rotten apple. To do this she must (A) pick up the apple, (B) horizontally move it across the table and (C) lower the apple into the trash. Identify for A, B, C situations when she is doing work. Explain your answer. A girl wants to throw away a rotten apple. To do this she must (A) pick up the apple, (B) horizontally move it across the table and (C) lower the apple into the trash. Identify for A, B, C situations when she is doing work. Explain your answer. A.) She has done work. The object is moving in the direct of her force. B.) She has done work. C.) She has not done work. Gravity did the work for her. The object is not moving in the direct of her force, but the direction of gravity's force.

B.) How much work does Rad do? Rad pushes a block 6 meters up an incline plane (ramp) using a force of 10N. Rad’s dad lifts straight up the same block to a height of 1 meter using a force of 60N. 1 m e t r A.) How much work does Rad’s dad Father do? W=F∙d W=60N∙1m W=60Nm B.) How much work does Rad do? W=F∙d W=10N∙60m W=60Nm

Suppose you want to get to the top of a hill Suppose you want to get to the top of a hill. Which path will require the least amount of work to get to the top? Path B Climbing up the steep hill Path A Walking up the long hill

Both paths require the same amount of work to get to the top. If you chose path A… then you are wrong! If you chose path B… then you are also wrong! Both paths require the same amount of work to get to the top.

How is this possible? Path A, while longer, requires less force (than B) against gravity to reach the top. Path B, while shorter, requires more force (than A)against the gravity to reach the top. Work Force Distance Work Force Distance Both paths require the same amount of work to get to the top.

Work Example 2 You lift a box with 10 Newtons of force onto a moving truck that is 1.5 meters high. How much work did you do? W = F x D W= 10 N x 1.5 m W= 15 Joules

Work Example 3 It takes 5 Newtons of force to push the same box onto a moving truck using a ramp that is 3 meters long. How much work did you do? (Assuming no friction on the ramp) W = F x D W= 5 N x 3 m W= 15 Joules In presence of friction, the work done in the ramp example would be higher but the force would still be lower since it is distributed over a ramp. The same amount of work is done but the ramp makes the work easier due to distribution of force.

As you saw from the previous examples: If you move the SAME object to the SAME location, it is the SAME WORK!