Force and Motion Lab Activity: Making Things Move!

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

Materials per Group:

• 1 small toy car
• ~1 foot of string
• Various small weights (washers, coins, paperclips)
• Ruler or measuring tape
• Masking tape (to mark starting line and measure distance)
• Stopwatch (optional, or use a phone)

Part 1: Observing Speeding Up

Instructions:

1. Tie one end of the string to the toy car and the other end to a small cup or bag where you can place weights.
2. Place the car at a starting line marked with masking tape on a smooth surface (like a table or floor).
3. Hang the cup with the string over the edge of the table so the cup can pull the car.
4. Prediction: What do you think will happen when you add a small weight to the cup?
   
   
   
   
   
   
   
5. Add one small weight to the cup. Release the car from the starting line and observe its motion.
6. Observation: Describe what happened to the car's speed. Did it speed up, slow down, or stay the same?
   
   
   
   
   
   
   
7. Now, add more weights to the cup (e.g., three weights total).
8. Prediction: How do you think adding more weights will change the car's motion compared to just one weight?
   
   
   
   
   
   
   
9. Release the car again. Observation: Describe what happened to the car's speed. How did it compare to using only one weight?
   
   
   
   
   
   
   

Thinking Questions:

• In this part, were the forces on the car balanced or unbalanced? How do you know?
  
  
  
  
  
  
  
• What caused the car to speed up? (Think about the weights!)
  
  
  
  
  
  
  

Part 2: Observing Slowing Down or Changing Direction (Optional, if time permits)

Instructions:

1. Set up the car as before, with a small weight in the cup to make it move across the table.

2. As the car is moving, gently place your hand in front of it to apply a small, opposite force. Do not stop it completely, just slow it down.

3. Observation: What happened to the car's speed when you applied an opposite force?
   
   
   
   
   
   
   

4. Now, try to gently push the car from the side while it's moving.

5. Observation: What happened to the car's direction when you pushed it from the side?
   
   
   
   
   
   
   

Thinking Questions:

• When you slowed the car down, were the forces on it balanced or unbalanced? Explain.
  
  
  
  
  
  
  
• When you made the car change direction, were the forces balanced or unbalanced? Why?
  
  
  
  
  
  
  

Conclusion

What did you learn about how unbalanced forces make objects accelerate? Give examples from your lab.

Predict the Motion Worksheet: What Happens Next?

Name: ________________________

Instructions: Read each scenario below and predict what will happen to the object's motion. Explain why you think it will move that way, using the terms "balanced forces," "unbalanced forces," and "accelerate" (speed up, slow down, or change direction).

Scenario 1: Tug-of-War

Two teams are playing tug-of-war. Team A pulls with 100 Newtons of force to the left, and Team B pulls with 80 Newtons of force to the right.

1. What is the net force? (Show your work)
   
   
   
   

2. Will the rope accelerate? If so, in which direction and how? (Speed up, slow down, or change direction?)
   
   
   
   
   
   
   

3. Explain your reasoning:
   
   
   
   
   
   
   
   
   
   
   
   

Scenario 2: Rolling Ball

A soccer ball is rolling across a flat, smooth field at a constant speed. Suddenly, a player kicks it hard from the side.

1. Before the kick, were the forces on the ball balanced or unbalanced?
   
   
   
   

2. After the kick, will the ball accelerate? If so, how?
   
   
   
   
   
   
   

3. Explain your reasoning:
   
   
   
   
   
   
   
   
   
   
   
   

Scenario 3: Falling Apple

An apple is hanging motionless from a tree branch. Suddenly, the stem breaks, and the apple falls towards the ground.

1. Before the stem broke, were the forces on the apple balanced or unbalanced?
   
   
   
   

2. After the stem broke, will the apple accelerate? If so, how?
   
   
   
   
   
   
   

3. Explain your reasoning:
   
   
   
   
   
   
   
   
   
   
   
   

Scenario 4: Rocket Launch

A rocket is sitting on the launchpad. The engines ignite, producing a massive upward thrust that is much greater than the force of gravity pulling it down.

1. Before engine ignition, were the forces on the rocket balanced or unbalanced?
   
   
   
   

2. After engine ignition, will the rocket accelerate? If so, how?
   
   
   
   
   
   
   

3. Explain your reasoning:
   
   
   
   
   
   
   
   
   
   
   
   

Answer Key for Predict the Motion Worksheet

Scenario 1: Tug-of-War

1. What is the net force? (Show your work)

   • Net force = 100 Newtons (left) - 80 Newtons (right) = 20 Newtons to the left.
     
     
     
     

2. Will the rope accelerate? If so, in which direction and how? (Speed up, slow down, or change direction?)

   • Yes, the rope will accelerate by speeding up to the left.
     
     
     
     
     
     
     

3. Explain your reasoning:

   • The forces are unbalanced because the net force is 20 Newtons to the left. Since there is a net force, the rope will accelerate in the direction of the greater force (Team A), causing it to speed up towards the left.
     
     
     
     
     
     
     
     
     
     
     
     

Scenario 2: Rolling Ball

1. Before the kick, were the forces on the ball balanced or unbalanced?

   • Balanced. If it's rolling at a constant speed, the forces are balanced (or negligible friction).
     
     
     
     

2. After the kick, will the ball accelerate? If so, how?

   • Yes, the ball will accelerate by changing direction and likely speeding up.
     
     
     
     
     
     
     

3. Explain your reasoning:

   • When the player kicks the ball from the side, an unbalanced force is applied. This causes the ball to accelerate by changing its direction of motion and potentially increasing its speed.
     
     
     
     
     
     
     
     
     
     
     
     

Scenario 3: Falling Apple

1. Before the stem broke, were the forces on the apple balanced or unbalanced?

   • Balanced. The force of gravity pulling it down was balanced by the tension in the stem pulling it up.
     
     
     
     

2. After the stem broke, will the apple accelerate? If so, how?

   • Yes, the apple will accelerate by speeding up towards the ground.
     
     
     
     
     
     
     

3. Explain your reasoning:

   • Once the stem breaks, the upward force (tension) is gone. The force of gravity is now an unbalanced force acting downwards. This causes the apple to accelerate by speeding up as it falls towards the Earth.
     
     
     
     
     
     
     
     
     
     
     
     

Scenario 4: Rocket Launch

1. Before engine ignition, were the forces on the rocket balanced or unbalanced?

   • Balanced. The force of gravity was balanced by the normal force from the launchpad.
     
     
     
     

2. After engine ignition, will the rocket accelerate? If so, how?

   • Yes, the rocket will accelerate by speeding up upwards.
     
     
     
     
     
     
     

3. Explain your reasoning:

   • When the engines ignite, the upward thrust creates an unbalanced force that is greater than the downward force of gravity. This net upward force causes the rocket to accelerate by speeding up as it moves upwards.