Net Force Worksheet
NYSSLS Standard MS-PS2-2
Net Force & Motion Lab
Investigating How Net Force and Mass Control Changes in Motion
Name: Date: Class:
Scientist's Word Toolbelt & Sentence Starters
Net Force (\(F_{\text{net}}\))
The total leftover force after combining all pushes and pulls. Same direction: add. Opposite directions: subtract.
Balanced vs. Unbalanced
Balanced: Net force is \(0\text{ N}\) (no change in motion).
Unbalanced: Net force is greater than \(0\text{ N}\) (motion changes).
Mass & Acceleration
Mass: How much matter is in an object.
Acceleration: Any change in speed (speeding up or slowing down) or direction.
Helpful Frames: "Because the forces are [balanced / unbalanced], the net force is ___ N, which causes the object to..." | "When mass increases, the same net force causes [more / less] change in motion."
Step 1: Finding the Sum of Forces (Balanced vs. Unbalanced) MS-PS2-2 Foundation
Guided Model: Drone in the Wind
Phenomenon: A weather drone hovers in the air. Its electric propellers push it forward with \(60\text{ N}\) of force. Suddenly, a headwind blows directly against it with \(40\text{ N}\) of force.
Step 1: Calculate Net Force
The forces point in opposite directions. Subtract the smaller force: \(60\text{ N} - 40\text{ N} = 20\text{ N}\) forward.
Step 2: Predict Motion Change
The forces are unbalanced (\(F_{\text{net}} > 0\text{ N}\)). The drone speeds up in the forward direction!
Phenomenon Case Study 1: The Hudson River Cargo Barge
Independent Practice
A heavy cargo barge floats on the Hudson River. Two small tugboats push forward together. Tugboat 1 pushes with \(5{,}000\text{ N}\) and Tugboat 2 pushes with \(3{,}000\text{ N}\). At the same time, the river water friction resists the barge by pushing backward with \(6{,}000\text{ N}\).
1. What is the net force acting on the cargo barge, and how will its motion change?
A \(14{,}000\text{ N}\) forward; barge moves at constant speed
B \(2{,}000\text{ N}\) forward; barge speeds up in the forward direction
C \(0\text{ N}\); barge stops moving completely
D \(2{,}000\text{ N}\) backward; barge slows down and moves backward
2. Later, Tugboat 2 shuts off its engine so only Tugboat 1 pushes forward (\(5{,}000\text{ N}\)), while water friction stays at \(6{,}000\text{ N}\) backward. Calculate the new net force and describe in complete sentences what will happen to the barge's speed.
Page 1 of 3 • MS-PS2-2 Sum of Forces Net Force & Motion Lab • Student Investigation
Step 2: Connecting Net Force, Mass, and Motion Changes Standard MS-PS2-2
The Two Main Rules of Motion Changes
Change in Motion = Net Force ÷ Mass
Rule A: Effect of Mass (Force is Constant)
If the push stays the same, adding more mass makes an object harder to speed up or slow down. Less mass means greater change in motion.
Rule B: Effect of Force (Mass is Constant)
If the mass stays the same, applying a greater net force creates a faster change in speed. Doubling force doubles acceleration.
Phenomenon Case Study 2: Arctic Supply Sled Trials
Experimental Data Table
Researchers in Greenland test motorized supply sleds across smooth, flat ice. They record how quickly the sled's speed changes in a \(5\text{-second}\) time window when they change either the sled's mass or the motor's net pulling force.
| Trial # |
Sled Mass |
Net Pull Force |
Starting Speed |
Speed After \(5\text{ s}\) |
Change in Speed (\(\Delta v\)) |
| Trial 1 |
\(100\text{ kg}\) |
\(200\text{ N}\) |
\(0\text{ m/s}\) |
\(10\text{ m/s}\) |
\(+10\text{ m/s}\) |
| Trial 2 |
\(200\text{ kg}\) (\(2\times\)) |
\(200\text{ N}\) |
\(0\text{ m/s}\) |
\(5\text{ m/s}\) |
\(+5\text{ m/s}\) (\(\frac{1}{2}\times\)) |
| Trial 3 |
\(400\text{ kg}\) (\(4\times\)) |
\(200\text{ N}\) |
\(0\text{ m/s}\) |
\(2.5\text{ m/s}\) |
\(+2.5\text{ m/s}\) (\(\frac{1}{4}\times\)) |
| Trial 4 |
\(100\text{ kg}\) |
\(400\text{ N}\) (\(2\times\)) |
\(0\text{ m/s}\) |
\(20\text{ m/s}\) |
\(+20\text{ m/s}\) (\(2\times\)) |
3. Look at Trials 1, 2, and 3. When the pulling force remained constant at \(200\text{ N}\), what happened to the change in speed each time the mass was doubled?
A The change in speed doubled
B The change in speed was cut in half
C The change in speed stayed exactly the same
D The sled moved backward
4. Compare Trial 1 and Trial 4. How did doubling the net force from \(200\text{ N}\) to \(400\text{ N}\) on the same \(100\text{ kg}\) sled affect its motion? Cite specific numbers from the table.
Page 2 of 3 • MS-PS2-2 Force & Mass Relationships Net Force & Motion Lab • Student Investigation
Step 3: Planning a Scientific Investigation Standard MS-PS2-2 Performance Task
Investigation Challenge: The Toy Rover Test Track
Your science group needs to design a laboratory investigation to provide experimental evidence that: "Increasing the mass of a toy car makes it harder to speed up when pulled by the same constant force."
A Identify Experimental Variables
Independent Variable
What one thing will you intentionally change between trials?
Dependent Variable
What will you measure to see the change in motion?
Controlled Variables
Name two conditions you must keep exactly the same:
B Write Your Investigation Procedure
Outline 3 clear steps your team will follow using a toy cart, metal weights, a spring scale (or hanging pulley weight), a stopwatch, and a meter stick.
Step 1:
Step 2:
Step 3:
C Design Your Data Table
Fill in the column headers you would use to record your observations and measurements during the test:
| Trial |
Cart Mass (\(\text{g}\)) |
[Column Header 2] |
[Column Header 3] |
| 1 |
100 g |
|
|
| 2 |
200 g |
|
|
| 3 |
300 g |
|
|
D Evidence-Based Conclusion & Reasoning
If your hypothesis is correct, complete the scientific reasoning statement explaining what your data will show:
Page 3 of 3 • MS-PS2-2 Investigation Planning Net Force & Motion Lab • Student Investigation
Net Force Answer Key
Teacher Resource • Scoring & Investigation Guide
Net Force & Motion Lab: Answer Key
Standard Alignment: NYSSLS MS-PS2-2 (Forces, Mass & Motion)
Total Points 20 Points
Critical Misconceptions to Address for MS-PS2-2
Common Misconception: Students often think that moving objects must always have an active net force in the direction of motion, or that constant speed requires an unbalanced push.
Scientific Truth (MS-PS2-2): If forces are balanced (\(F_{\text{net}} = 0\text{ N}\)), an object keeps moving at a constant speed in a straight line. Unbalanced forces cause changes in motion (speeding up or slowing down).
Step 1 Solutions: Sum of Forces (Balanced vs. Unbalanced) 6 Points Possible
Question 1: Cargo Barge Net Force [2 Points] Correct: Option B
Correct Answer: B (\(2{,}000\text{ N}\) forward; barge speeds up in the forward direction)
Step-by-Step Mathematical Reasoning
1. Combine forces in the same direction: \(F_{\text{forward}} = 5{,}000\text{ N} + 3{,}000\text{ N} = 8{,}000\text{ N}\).
2. Subtract opposing friction force: \(F_{\text{net}} = 8{,}000\text{ N} - 6{,}000\text{ N} = 2{,}000\text{ N}\) forward.
3. Because \(F_{\text{net}} > 0\text{ N}\) forward, the forces are unbalanced, causing the barge to accelerate forward.
Question 2: Tugboat Engine Shut Off [4 Points] Short Response Rubric
Exemplar Student Response
"The new net force is \(1{,}000\text{ N}\) in the backward direction (\(5{,}000\text{ N} - 6{,}000\text{ N} = -1{,}000\text{ N}\)). Because the net force now opposes the barge's forward motion, the forces are unbalanced and will cause the barge to slow down (decelerate)."
Grading Criteria (4 pts):
- Correct calculation: \(1{,}000\text{ N}\) (1 pt)
- Identifies direction: backward / opposing motion (1 pt)
- States forces are unbalanced (1 pt)
- Concludes that the barge slows down (1 pt)
Scaffolding Prompt for Struggling Learners:
Ask: "Which force is bigger now—the forward push (\(5{,}000\text{ N}\)) or the backward drag (\(6{,}000\text{ N}\))? If backward is bigger, will it speed up or slow down?"
Teacher Key • Page 1 of 3 (MS-PS2-2 Sum of Forces) Net Force & Motion Lab • Teacher Scoring Guide
Part 2 Answer Key & Guide
Step 2: Connecting Net Force, Mass, and Motion Changes
6 Points Possible
Mathematical Proportionality Reference (\(a = \frac{F_{\text{net}}}{m}\)):
Mass vs. Acceleration (Inverse): With \(F_{\text{net}} = 200\text{ N}\):
• \(100\text{ kg} \rightarrow a = 2.0\text{ m/s}^2\) (\(\Delta v = +10\text{ m/s}\))
• \(200\text{ kg} \rightarrow a = 1.0\text{ m/s}^2\) (\(\Delta v = +5\text{ m/s}\))
• \(400\text{ kg} \rightarrow a = 0.5\text{ m/s}^2\) (\(\Delta v = +2.5\text{ m/s}\))
Force vs. Acceleration (Direct): With \(m = 100\text{ kg}\):
• \(200\text{ N} \rightarrow a = 2.0\text{ m/s}^2\) (\(\Delta v = +10\text{ m/s}\))
• \(400\text{ N} \rightarrow a = 4.0\text{ m/s}^2\) (\(\Delta v = +20\text{ m/s}\))
Doubling force exactly doubles the change in speed!
Question 3: Mass Doubling Effect on Speed Change [2 Points] Correct: Option B
Correct Answer: B (The change in speed was cut in half)
Reasoning & Data Evidence
In Trial 1 (\(100\text{ kg}\)), \(\Delta v = 10\text{ m/s}\). In Trial 2 (\(200\text{ kg}\)), \(\Delta v = 5\text{ m/s}\). In Trial 3 (\(400\text{ kg}\)), \(\Delta v = 2.5\text{ m/s}\). Each time mass is doubled, the change in speed over the same 5-second interval is exactly halved.
Question 4: Comparing Trial 1 & Trial 4 (Effect of Force) [4 Points] Data Evidence Rubric
Exemplar Student Response
"When the net force was doubled from \(200\text{ N}\) in Trial 1 to \(400\text{ N}\) in Trial 4 on the same \(100\text{ kg}\) sled, the change in speed doubled from \(+10\text{ m/s}\) to \(+20\text{ m/s}\). This proves that when mass is held constant, change in speed is directly proportional to the net force applied."
Scoring Breakdown (4 pts):
- States that change in speed doubled (1 pt)
- Cites specific force numbers (\(200\text{ N}\) vs \(400\text{ N}\)) (1 pt)
- Cites specific speed numbers (\(10\text{ m/s}\) vs \(20\text{ m/s}\)) (1 pt)
- Mentions mass was kept constant at \(100\text{ kg}\) (1 pt)
Classroom Follow-Up Question:
"What would happen if we used 800 N of force on the 100 kg sled?" (Expected answer: \(\Delta v = +40\text{ m/s}\) in 5 s).
Teacher Key • Page 2 of 3 (MS-PS2-2 Data Analysis) Net Force & Motion Lab • Teacher Scoring Guide
Part 3 Performance Task Key
Investigation Planning Rubric (NYSSLS MS-PS2-2)
8 Points Possible
Section A: Experimental Variables [2 Points] All 3 Identified Correctly
Independent Variable: Mass of the cart (e.g. adding 100g, 200g, 300g weights).
Dependent Variable: Change in motion / time to cross 1 meter / final speed.
Controlled Variables (Any 2): Constant pull force, track surface/friction, starting at rest (0 m/s), distance.
Section B: Step-by-Step Procedure [2 Points] Exemplar Protocol
Step 1: Set up a 1-meter smooth track. Attach a string and constant 50 g hanging weight over a pulley (or pull with a spring scale held steady at \(0.5\text{ N}\)).
Step 2: Release the empty \(100\text{ g}\) cart from rest and time how many seconds it takes to travel the 1-meter mark using a stopwatch.
Step 3: Repeat the test adding \(100\text{ g}\) of mass (total \(200\text{ g}\)), and then adding another \(100\text{ g}\) (total \(300\text{ g}\)), keeping the pull force identical. Record all times.
Section C: Data Table Setup [2 Points] Table Design
Students must label both columns with appropriate variables and units:
Accepted Column Header 2: "Pulling Force (\(\text{N}\))" OR "Net Force (\(\text{N}\))" (Values must show a constant amount, e.g., \(0.5\text{ N}\) for all rows). Accepted Column Header 3: "Travel Time (\(\text{s}\))" OR "Change in Speed (\(\text{m/s}\))" OR "Acceleration (\(\text{m/s}^2\))".
Section D: Evidence-Based Conclusion [2 Points] CER Alignment
Exemplar Student Conclusion:
"The experimental data will show that as the cart's mass increased from \(100\text{ g}\) to \(300\text{ g}\), the time required to travel 1 meter increased (or the final speed decreased). This provides evidence that when net force is held constant, objects with more mass experience a smaller change in motion (less acceleration) because greater mass resists changes in velocity."
Materials Needed for Physical Classroom Execution:
Dynamics carts (or low-friction toy cars), set of slotted weights or washers (\(50\text{g}\)–\(100\text{g}\)), spring scales (\(0\)–\(5\text{ N}\)) or string with small hanging weights over desk pulleys, stopwatches or smartphone slow-motion cameras, meter sticks, masking tape for start/finish lines.
Teacher Key • Page 3 of 3 (Investigation Rubric) Net Force & Motion Lab • Teacher Scoring Guide
