MC

Physics

Standard: 02

Objective:  01.  Analyze forces acting on an object.

ILO:

 

 

You would like to measure the amount of friction present when sliding a block across the floor.  Which of the following instruments would be most helpful in measuring the friction?

a.  Triple beam balance

b.  Smart pulley

c.  Photogate

d.  Spring scale

e.  Meter stick

 

Correct Answer:  e

 

 

I

Physics

Standard: 02

Objective:  01.  Analyze forces acting on an object.

ILO:

 

 

A popular ride at the local amusement park is the log flume.  In this ride the rider is placed in a boat designed to resemble a large log.  The log with riders is moved along a water way until it is taken to the top of an incline.  From the top of the incline the log is released.  At the bottom of the incline the log returns to the water way from which the ride originated.

Answer the following questions.

1.  What is the purpose of the water at the bottom of the flume? (Other than to float the boat.)

 

2.  Describe the forces the participant will feel at each of the labeled points (A through F) as he/she moves around the course, up the incline, down the incline and finally stops at the bottom.

 

Correct Answers:

1.  The water absorbs the kinetic energy of the boat and provides a safe stop. (1 point)

2.  Forces felt:

            A: Starting out from rest, small accelerating force. (1 point)

            B: Moving around curves, small centripetal force.  (1 point)

            C: Starting up the incline, small accelerating force. (1 point)

            D: Dropping down the incline, accelerating force due to gravity. (1 point)

            E: Stopping at the bottom, large decelerating force. (1 point)

 

 

I

Physics

Standard: 02

Objective:  01.  Analyze forces acting on an object.

ILO:

 

 

A steel block is pulled along a steel surface.  An experiment is conducted that compares the forces needed to overcome friction when the weight is changed.

 

Block weights

5kg

10kg

15kg

Smooth steel surface

0.75kg

1.5kg

2.25kg

 

Answer the following questions as they relate to the above.

 

1.  What happens to the frictional force as the weight of the block increases?

            a.  The frictional force stays the same.

            b.  The frictional force increases.

            c.  The coefficient of friction increases.

            d.  The coefficient of friction decreases.

 

 

2.  Which graph depicts the change in frictional force of the smooth steel surface?

 

Correct Answers:

            1.  b

            2.  c

 

P

Physics

Standard: 02

Objective:  01.  Analyze forces acting on an object.

ILO:

 

 

Personal Power

 

Time Required:

Two class periods

 

Materials:

            1 chair for each group

            1 timing device for each group

            1 meter stick for each group

 

Background Information:

Students should be able to make metric measurements of length and have a basic understanding of mass, acceleration, force, work, energy and energy conversions.

 

 

 

Scoring Guide:

Score studentês work on the attached –Personal Power Scoring Form”.  Use the key to evaluate each studentês performance.  Evidence of how students have done on many –abilities” will be found in their written answers in the –Analysis” section.  Other evidence will come from observation of individuals and groups during the performance of the task.  For example, evidence of a studentês ability to –make estimates and approximations” will be found in his or her response to question 3 in the analysis section.

As you assign students this task, make sure they understand the abilities to be measured and how you will determine each studentês abilities.  Do not forget to mark the rating form as students work on those abilities that require direct observation of them at work.  Do not leave judgments until later.

 

Correct Answers:

Analysis:

1.  More power in 90 seconds.  Power is changed by the time.

2.  More work in less time.

3.  Most likely horsepower will decrease due to time increase.  (Accept most answers if explanation fits answer)

4.  Power is work, but time is factored in.  Power = work/time

5.  (Accept most answers if explanation fits answer)
Personal Power

 

Name: ____________________________________  Date: ____________________

Class/Period: ____________________  Total Score: ________________

 

Problem:

How much power can you generate?

 

Prediction:

How much horse power do you think you can generate in 30 seconds? _________  90 seconds? _________

 

Procedure:

1.  As a group of three designate one person as the timer, one as the stepper, and one as the chair holder and step counter.

2.  Determine the force of the stepper using the following information:

           

            There are roughly 2.2 pounds in 1 kilogram, so

           

                        Weight (pounds)

                        Mass (kilograms)  =  ___________

 

            Acceleration due to gravity is a constant: 9.8 m/s2

 

            Force = mass x acceleration (Newtonês 2nd law of motion), so

            Stepperês Force = mass (kilograms) x acceleration (gravity)

 

            Force of Stepper = _______________ kg. m/s2 or N (newtons)

 

3.  Determine the height of the chair in meters using the meter stick provided:

 

            Height of the chair = _______________ meters

 

Note: To see how much power you can generate, the stepper should step u onto the chair with one foot, then the other foot.  When both feet are on the chair, the stepper should immediately step down with one foot, then the other.  This should be done as fast as possible but do not jump up onto, or down from, the chair.

 

4.  Record, in the Data Table below, the number of times the stepper can step up onto the chair in 30 seconds.

5.  Record, in the Data Table below, the number of times the stepper can step up onto the chair in 90 seconds.

 

 

Steps

30 Seconds

 

90 Seconds

 

 

6.  Calculate the work for 30 seconds and 90 seconds.  Remember that work = force x distance.  You have the force of the stepper and you can calculate the distance from the number of steps times the height of the chair.

 

Note:  You are only doing work when you are stepping up onto the chair, so when determining distance you should multiply the number of times the stepper moves up onto the chair times the height of the chair in meters.  Do not include the distance to step down from the chair.

 

Work for 30 seconds: _____________ N-m or J (Joules)

Work for 90 seconds: _____________ N-m or J (Joules)

 

7.  Calculate the power for 30 seconds and 90 seconds.  Remember that power = work/time.

 

Power for 30 seconds: ____________ J/s or W (Watts)

Power for 90 seconds: ____________ J/s or W (Watts)

 

8.  One horsepower is approximately equal to 750 Watts.  Calculate the horsepower of the stepper.

 

Horsepower for 30 seconds: _____________ hp
Horsepower for 90 seconds: _____________ hp

 

 

This portion of the task is to be done by each individual in the group separately.

Analysis:

1.  Compare the amount of power produced in 30 seconds with the amount produced in 90 seconds.  What do you think accounts for the results?

 

 

 

2.  What would the stepper have done to create more horsepower?  Explain your answer.

 

 

 

3.  Predict what horsepower the stepper would generate, if they followed the same procedure used in this exercise, over a 3-minute period.  Explain your answer.

 

 

 

4.  In your own words, describe power and explain how it is different from work.  Also include the formula.

 

 

 

5.  Give three examples of how you use power in your life.  Where does that power come from?