Lab 4: Static Equilibrium
Name Date
Assignment Submission Directions: Download this assignment sheet and complete by answering all questions.
You will need to access the simulations website in order to complete the labs. When completed, save your work
and upload the document to the Assignment Upload for graded submission. 50 points.
Items in red font require submission into a pre populated text box shown as Click here to enter text. (Note: you
do not need to fill this one in, for directions purposes only.)
Part A: Exploring Static Equilibrium
Simulation Website: https://phet.colorado.edu/en/simulation/forces-and-motion-basics
Learning Goals
● Identify when forces are balanced vs unbalanced.
● Determine the sum of forces (net force) on an object with more than one force on it.
● Predict the motion of an object with zero net force.
● Predict the direction of motion given a combination of forces.
Activity
Part 1: Exploring Forces and Static Forces
● Load the simulation website.
● Select Friction Option.
● Set Bar to ‘Lots’.
● Check the ‘Speed’ button to show speedometer.
● UNCHECK all the other boxes for now, INCLUDING
the “FORCES” box.
1. Change the applied force and watch the motion of the box. Determine the size of the friction force acting
on the box when it slides (the kinetic friction force).
When the applied force was reduced below 188 N, the speedometer shows that the speed of the box was
decreasing, from these observations, the size / magnitude of the kinetic friction force is 188 N.
2. Explain what you did to figure this force out based on observations of the motion of the box.
We gradually increased the force (starting with 50 N intervals and adjusting based on the box’s motion), the box
began to move when the applied force reached 251 N. At that point, the speedometer was turning clockwise,
showing the speed was increasing. Then, I slowly decreased the force, and when it dropped to 188 N, the
speedometer stopped moving, meaning the speed stayed the same. When the force went below 188 N, the
speedometer turned counter-clockwise, showing the box was slowing down. From this, I figured out that the
kinetic friction force is 188 N.
3. Explore the simulation to figure out how large the maximum force of static friction is on the box (for the “Lots”
of friction case). Explain what you did and report the value you found.
To find the maximum static friction force on the box, I increased the applied force little by little to see the exact
point right before the box started moving. I found that the maximum static friction force is 250 N because the box
only started moving when the applied force reached 251 N.
4. Now activate the “Forces” box and the “Sum of forces” check boxes. Keep friction at “Lots”. Push the box with
max force until the speedometer hits its max value. Describe what happens noting directions the box moves.
When the box was pushed with a maximum force of 500 N, it accelerated quickly until it reached a top speed of
, Lab 4: Static Equilibrium
person pushing the box falls off (or "dies"). Even though the person is gone, the box keeps moving at a constant
speed of 40 m/s without accelerating. Since there’s no one left to push, no more force is applied, so the box
doesn’t speed up anymore.
6. Keeping all the settings the same as #5, try to stop the coasting box by applying forces. Explain why it is
difficult to get the box to come to a complete stop.
It was almost impossible to get the box to stop completely. Even when I adjusted the simulation to lower the
speed and removed the applied force, the box kept moving at a constant speed. This happened because there
was no friction in the simulation to resist or stop the box's motion, so it just kept going without slowing down.
7. Keeping settings the same as #5, now stack the extra box (just to the left of the applied force setting) on top of
the first box. Repeat the tasks of #5 and #6. What is different about these tasks now that the mass of the object is
doubled? What is the same?
The difference in this case is that the crates take twice as long to reach a speed of 40 m/s at a steady, constant
rate. This happens because the acceleration is cut in half compared to the earlier scenario without the second
crate on top. What stays the same is the applied force and the friction force, both of which remain at 0.
8. Reset the Friction app. Make sure Forces and Speed are checked. Describe what you observe in the data table.
Applied Force (N) Motion Description
50 he crate is not moving, remains stationary.
100 The crate is not moving, remains stationary.
150 The crate begins acceleration forward until velocity of 40 m/s, then the crate slows down
to a stationary position because of the friction force
9. Check the box that says “Sum of Forces”. Repeat procedures step 8.
Applied Force (N) Sum of Forces Value (taken from simulation)
50 Sum of forces = 0, crate is stationary and friction force and applied force are the same.
100 Sum of forces = 0, crate is stationary and friction force and applied force are the same.
150 Sum of forces = 56, crate begins to move, applied force is larger than friction force which
explains why the crate began moving.
10. Compare your results across data tables. Determine if there is any noticeable pattern or statement you can
write comparing the motion descriptions with the Sum of Forces values for each applied force (50, 100, 150).
When comparing my data, I noticed a pattern showing that there’s a maximum threshold for the friction force
opposing the applied force. If the applied force is below this threshold, the friction cancels it out, making the
sum of forces equal to 0, so there’s no acceleration. However, if the applied force goes above this threshold, the
sum of forces increases, causing the crate to accelerate or move forward.
11. Newton’s Second Law states “The acceleration of an object as produced by a net force is directly proportional
to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass
of the object.” Explain how your observations relate to Newton’s Second Law (hint, you might want to look up the
definition of the word “net”).
According to Newton's 2nd law of motion, our observations match the law, which states that acceleration is
inversely proportional to mass. This is true because when the applied force is below the maximum threshold of
friction force, the opposing forces cancel each other out, making the sum of forces equal to 0 and resulting in no
acceleration. We saw this in the simulation when adding a second crate on top of the first, which doubled the
mass and caused the acceleration to be cut in half.
12. Reset the app. Check the force and speed box. Apply 50 N of force to the crate. Slowly click (in 50 N
increments) to increase the amount of applied force until the crate starts to move/accelerate. Note the range
of force values when the crate first started to move. Record this range below (e.g. starts moving somewhere
between 0 and 50 N).
The crate began to move forward / accelerate within the range of 100 – 150 N.
13. Reset the app. Repeat the steps in “a”. Once you have just made the crate move do not adjust the force any
Name Date
Assignment Submission Directions: Download this assignment sheet and complete by answering all questions.
You will need to access the simulations website in order to complete the labs. When completed, save your work
and upload the document to the Assignment Upload for graded submission. 50 points.
Items in red font require submission into a pre populated text box shown as Click here to enter text. (Note: you
do not need to fill this one in, for directions purposes only.)
Part A: Exploring Static Equilibrium
Simulation Website: https://phet.colorado.edu/en/simulation/forces-and-motion-basics
Learning Goals
● Identify when forces are balanced vs unbalanced.
● Determine the sum of forces (net force) on an object with more than one force on it.
● Predict the motion of an object with zero net force.
● Predict the direction of motion given a combination of forces.
Activity
Part 1: Exploring Forces and Static Forces
● Load the simulation website.
● Select Friction Option.
● Set Bar to ‘Lots’.
● Check the ‘Speed’ button to show speedometer.
● UNCHECK all the other boxes for now, INCLUDING
the “FORCES” box.
1. Change the applied force and watch the motion of the box. Determine the size of the friction force acting
on the box when it slides (the kinetic friction force).
When the applied force was reduced below 188 N, the speedometer shows that the speed of the box was
decreasing, from these observations, the size / magnitude of the kinetic friction force is 188 N.
2. Explain what you did to figure this force out based on observations of the motion of the box.
We gradually increased the force (starting with 50 N intervals and adjusting based on the box’s motion), the box
began to move when the applied force reached 251 N. At that point, the speedometer was turning clockwise,
showing the speed was increasing. Then, I slowly decreased the force, and when it dropped to 188 N, the
speedometer stopped moving, meaning the speed stayed the same. When the force went below 188 N, the
speedometer turned counter-clockwise, showing the box was slowing down. From this, I figured out that the
kinetic friction force is 188 N.
3. Explore the simulation to figure out how large the maximum force of static friction is on the box (for the “Lots”
of friction case). Explain what you did and report the value you found.
To find the maximum static friction force on the box, I increased the applied force little by little to see the exact
point right before the box started moving. I found that the maximum static friction force is 250 N because the box
only started moving when the applied force reached 251 N.
4. Now activate the “Forces” box and the “Sum of forces” check boxes. Keep friction at “Lots”. Push the box with
max force until the speedometer hits its max value. Describe what happens noting directions the box moves.
When the box was pushed with a maximum force of 500 N, it accelerated quickly until it reached a top speed of
, Lab 4: Static Equilibrium
person pushing the box falls off (or "dies"). Even though the person is gone, the box keeps moving at a constant
speed of 40 m/s without accelerating. Since there’s no one left to push, no more force is applied, so the box
doesn’t speed up anymore.
6. Keeping all the settings the same as #5, try to stop the coasting box by applying forces. Explain why it is
difficult to get the box to come to a complete stop.
It was almost impossible to get the box to stop completely. Even when I adjusted the simulation to lower the
speed and removed the applied force, the box kept moving at a constant speed. This happened because there
was no friction in the simulation to resist or stop the box's motion, so it just kept going without slowing down.
7. Keeping settings the same as #5, now stack the extra box (just to the left of the applied force setting) on top of
the first box. Repeat the tasks of #5 and #6. What is different about these tasks now that the mass of the object is
doubled? What is the same?
The difference in this case is that the crates take twice as long to reach a speed of 40 m/s at a steady, constant
rate. This happens because the acceleration is cut in half compared to the earlier scenario without the second
crate on top. What stays the same is the applied force and the friction force, both of which remain at 0.
8. Reset the Friction app. Make sure Forces and Speed are checked. Describe what you observe in the data table.
Applied Force (N) Motion Description
50 he crate is not moving, remains stationary.
100 The crate is not moving, remains stationary.
150 The crate begins acceleration forward until velocity of 40 m/s, then the crate slows down
to a stationary position because of the friction force
9. Check the box that says “Sum of Forces”. Repeat procedures step 8.
Applied Force (N) Sum of Forces Value (taken from simulation)
50 Sum of forces = 0, crate is stationary and friction force and applied force are the same.
100 Sum of forces = 0, crate is stationary and friction force and applied force are the same.
150 Sum of forces = 56, crate begins to move, applied force is larger than friction force which
explains why the crate began moving.
10. Compare your results across data tables. Determine if there is any noticeable pattern or statement you can
write comparing the motion descriptions with the Sum of Forces values for each applied force (50, 100, 150).
When comparing my data, I noticed a pattern showing that there’s a maximum threshold for the friction force
opposing the applied force. If the applied force is below this threshold, the friction cancels it out, making the
sum of forces equal to 0, so there’s no acceleration. However, if the applied force goes above this threshold, the
sum of forces increases, causing the crate to accelerate or move forward.
11. Newton’s Second Law states “The acceleration of an object as produced by a net force is directly proportional
to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass
of the object.” Explain how your observations relate to Newton’s Second Law (hint, you might want to look up the
definition of the word “net”).
According to Newton's 2nd law of motion, our observations match the law, which states that acceleration is
inversely proportional to mass. This is true because when the applied force is below the maximum threshold of
friction force, the opposing forces cancel each other out, making the sum of forces equal to 0 and resulting in no
acceleration. We saw this in the simulation when adding a second crate on top of the first, which doubled the
mass and caused the acceleration to be cut in half.
12. Reset the app. Check the force and speed box. Apply 50 N of force to the crate. Slowly click (in 50 N
increments) to increase the amount of applied force until the crate starts to move/accelerate. Note the range
of force values when the crate first started to move. Record this range below (e.g. starts moving somewhere
between 0 and 50 N).
The crate began to move forward / accelerate within the range of 100 – 150 N.
13. Reset the app. Repeat the steps in “a”. Once you have just made the crate move do not adjust the force any
