Force and Motion Lab Activity: Let the Motion Begin!

Objective: To observe and demonstrate how unbalanced forces cause an object to accelerate (speed up, slow down, or change direction).

Materials:

• Toy car or object with wheels
• String
• Various weights (e.g., washers, small books, paperclips)
• Ruler or measuring tape
• Stopwatch or timer
• Masking tape (to mark starting lines)
• (Optional) Pulley system

Safety First! Always handle materials carefully. Do not throw or misuse any lab equipment.

Part 1: Exploring Changes in Speed (Speeding Up)

Procedure:

1. Set up: Place your toy car on a flat surface. Use masking tape to mark a starting line.
2. Scenario A: Gentle Push
   • Gently push the car forward for a short distance. Observe its motion.
   • What happened to the car's speed when you pushed it?
     
     
     
3. Scenario B: Stronger Push
   • Push the car forward with more force than in Scenario A. Observe its motion.
   • How did the car's speed compare to Scenario A? Why do you think this happened?
     
     
     
4. Scenario C: Adding Weight (and a pull)
   • Tie one end of a string to the toy car and the other end to a small weight (e.g., 2-3 washers). Allow the weight to hang over the edge of the table (or over a pulley if you have one).
   • Release the car from the starting line and observe its motion. Measure the time it takes to travel a certain distance (e.g., 50 cm).
   • Describe the car's motion. Was it speeding up, slowing down, or moving at a constant speed?
     
     
     
5. Scenario D: More Weight (more pull)
   • Add more weight to the string (e.g., double the washers). Repeat the experiment from Scenario C, releasing the car from the same starting line and measuring the time to travel the same distance.
   • How did the car's motion compare to Scenario C? What does this tell you about the relationship between force and speed?
     
     
     

Part 2: Exploring Changes in Speed (Slowing Down/Stopping)

Procedure:

1. Scenario E: Friction
   • Give the toy car a push on the flat surface. Observe what happens to its speed over time without any further pushes or pulls.
   • What caused the car to eventually slow down and stop? What force is at play here?
     
     
     
2. Scenario F: Gentle Resistance
   • Give the car a push. As it's moving, gently place your hand in front of it to slow it down. Do not stop it completely, just slow it.
   • How did applying a force in the opposite direction affect the car's motion?
     
     
     

Part 3: Exploring Changes in Direction

Procedure:

1. Scenario G: Direct Hit
   • Roll the toy car in a straight line. As it's moving, gently tap the side of the car with your finger.
   • What happened to the car's path? Why did it change direction?
     
     
     
2. Scenario H: Obstacle Course (Optional)
   • Set up a simple obstacle (e.g., a book or a pencil) in the path of the car. Roll the car towards the obstacle.
   • What happens when the car collides with the obstacle? How does the obstacle apply an unbalanced force?
     
     
     

Discussion Questions (to be answered with your group):

1. In which scenarios did the toy car accelerate by speeding up? What caused this to happen?
   
   
   
   
   
2. In which scenarios did the toy car accelerate by slowing down? What caused this to happen?
   
   
   
   
   
3. In which scenarios did the toy car accelerate by changing direction? What caused this to happen?
   
   
   
   
   
4. How did the concept of unbalanced forces apply to all the changes in motion you observed in the lab? Give specific examples.
   
   
   
   
   
   
   
   
5. Can an object accelerate without an unbalanced force acting on it? Explain your reasoning.
   
   
   
   
   

Predict the Motion Worksheet

Name: _________________________ Date: _________________________

Instructions: Read each scenario carefully. Predict what will happen to the object's motion (will it speed up, slow down, change direction, or stay the same?). Then, explain why based on what you've learned about balanced and unbalanced forces and acceleration.

Scenario 1: Kicking a Stationary Soccer Ball

• Description: A soccer player kicks a soccer ball that is sitting still on the grass.
• Prediction: What will happen to the soccer ball's motion?
  
  
  
• Explanation: Why? (Mention forces involved)
  
  
  
  
  

Scenario 2: Car Braking at a Stop Sign

• Description: A car is driving down a street and the driver applies the brakes to stop at a stop sign.
• Prediction: What will happen to the car's motion?
  
  
  
• Explanation: Why? (Mention forces involved)
  
  
  
  
  

Scenario 3: Pushing a Box Across a Rough Floor

• Description: You are pushing a heavy box across a very rough concrete floor at a constant speed.
• Prediction: If you suddenly stop pushing, what will happen to the box's motion?
  
  
  
• Explanation: Why? (Mention forces involved)
  
  
  
  
  

Scenario 4: Turning a Bicycle

• Description: You are riding your bicycle in a straight line, and then you steer the handlebars to make a sharp turn to the right.
• Prediction: What will happen to your bicycle's motion?
  
  
  
• Explanation: Why? (Mention forces involved)
  
  
  
  
  

Scenario 5: Book on a Shelf

• Description: A book is sitting perfectly still on a flat shelf.
• Prediction: What will happen to the book's motion if no one touches it?
  
  
  
• Explanation: Why? (Mention forces involved)
  
  
  
  
  

Challenge Question:

Describe a situation where an object is moving but NOT accelerating. Explain how this is possible in terms of forces.

Answer Key for Predict the Motion Worksheet

Instructions: This answer key provides correct responses and explanations for the "Predict the Motion Worksheet." Remember to encourage students to explain their reasoning, as multiple correct explanations may exist.

Scenario 1: Kicking a Stationary Soccer Ball

• Prediction: The soccer ball will speed up and change direction (from still to moving in the direction of the kick).
• Explanation: When the player kicks the ball, an unbalanced force (the kick) is applied. This net force causes the ball to accelerate, both by increasing its speed from zero and by moving it in a specific direction. The force of the kick is greater than any friction or air resistance initially acting on the still ball.

Scenario 2: Car Braking at a Stop Sign

• Prediction: The car will slow down and eventually stop.
• Explanation: When the driver applies the brakes, an unbalanced force (friction from the brakes on the wheels, and between the tires and the road) acts in the opposite direction of the car's motion. This net force causes the car to decelerate (slow down), until it comes to a stop.

Scenario 3: Pushing a Box Across a Rough Floor

• Prediction: If you stop pushing, the box will slow down and eventually stop.
• Explanation: When you stop pushing, the applied force from your push is removed. However, the force of friction between the box and the rough floor is still acting on the box, now as an unbalanced force opposing its motion. This net force of friction causes the box to decelerate (slow down) until it reaches a complete stop.

Scenario 4: Turning a Bicycle

• Prediction: Your bicycle will change direction.
• Explanation: When you steer the handlebars, you apply a force that causes the bicycle to lean and turn. This creates an unbalanced force (a centripetal force from the ground pushing on the tires) perpendicular to your current direction of motion. This net force causes the bicycle to accelerate by changing its direction, even if its speed remains constant.

Scenario 5: Book on a Shelf

• Prediction: The book will stay still.
• Explanation: The book will remain still because the forces acting on it are balanced. Gravity pulls the book down, but the shelf pushes up on the book with an equal and opposite force (normal force). The net force on the book is zero, so its motion does not change.

Challenge Question:

Describe a situation where an object is moving but NOT accelerating. Explain how this is possible in terms of forces.

• Answer: An object is moving but NOT accelerating when it is moving at a constant speed in a straight line. This is possible when all the forces acting on the object are balanced, meaning the net force is zero.
• Example: A car cruising on a highway at a steady 60 mph on a straight road. The forward thrust from the engine is balanced by the forces of air resistance and friction. Because the forces are balanced, there is no net force, and therefore no acceleration (no change in speed or direction). Another example is an object floating in space far from any gravitational pull, moving at a constant velocity.