Get the Gizmo ready:

Question

Click Reset.
Remove all fans from the cart.
Question: What happens to the cart when there is no force?

Form hypothesis: What will the cart's motion be like when there is no force at all? (There is no friction in this model.)

Write your hypothesis as "If there is no force then (your answer here) because (your answer here)."

(1 point)
If there is no force then..., because ...

2. Predict: Suppose a cart with no fans has a starting velocity of 2 m/s. What will be the velocity of the cart when it reaches the wall? (1 point)

3. Experiment: Check that there are no fans on the cart. On the DESCRIPTION tab, set the Initial velocity of the cart to 2.0 m/s. Select the BAR CHART tab, and click Play.

What do you notice about the velocity of the cart?
(1 point)

4. Experiment: Click Reset. Place two fans on the cart, and point them in opposite directions. (Next to DIRECTION, click the 2015-03-13_11-22-47 button for one fan.) Turn both fans on, and click Play.

What do you notice about the velocity of the cart?
(1 point)

5A. Analyze: Select the GRAPH tab.

What do you notice about the graph of position vs. time (x vs t)?
(1 point)

5B. What does the velocity vs. time (v vs t) graph show? (1 point)

5C. What do you notice about the graph of acceleration vs. time (a vs t)? (1 point)

6. Draw conclusions: Newton’s first law states that an object in motion will travel at a constant velocity unless acted upon by an unbalanced force. How do these experiments show this?

(2 points)

Answer 1

1. Form hypothesis: If there is no force then the cart will continue moving at a constant velocity because an object in motion remains in motion unless acted upon by an unbalanced force.

2. Predict: The velocity of the cart when it reaches the wall will still be 2 m/s because there is no force acting on it to change its velocity in the absence of friction.

3. Experiment Observation: The velocity of the cart remains constant at 2 m/s throughout its motion until it reaches the wall.

4. Experiment Observation: The velocity of the cart fluctuates or is zero when the fans are turned on in opposite directions, indicating that the forces are canceling each other out.

5A. Position vs. Time Graph Observation: The graph of position vs. time (x vs. t) shows a straight line when there are no fans, indicating uniform motion. When fans are turned on in opposite directions, the graph may show a leveling off or a more variable line depending on how effectively the forces cancel.

5B. Velocity vs. Time Graph Observation: The velocity vs. time (v vs. t) graph shows a constant velocity when there are no fans and remains flat at 2 m/s. With the two fans turned on, there may be a fluctuation about a central value or a return to zero velocity, indicating that the net force is effectively zero.

5C. Acceleration vs. Time Graph Observation: The acceleration vs. time (a vs. t) graph shows zero acceleration when there are no forces acting on the cart. With the two fans going in opposite directions, this could also show near zero acceleration as the forces balance out.

6. Draw conclusions: These experiments illustrate Newton’s first law by demonstrating that when no unbalanced forces act on the cart, it maintains a constant velocity. In the first case, the constant speed indicates that with no forces (friction or propulsion), the cart does not slow down or change direction. When both fans are active but counteracting, the forces are balanced, resulting in no change in velocity, again demonstrating that the cart does not accelerate without an unbalanced force.