In a situation in which a single force acts on an object, the net force is simply the same as that Fan 30 single force. For example, for the cart shown here, the net force is simply 30 N pushing it to the right. Summarizing Questions S1. a) When an unbalanced combination of forces acts on an object (either at rest or in motion), does the speed of the object change, or does it remain constant? b) Why does it make sense that this is the same as the effect of a single force?Activity 1: Combinations of Forces O $2. Shown below are two force diagrams for a cart that is already moving. What would the motion of each cart be like? Explain your reasoning. S3. In a previous class a student made the following statement: "When more than one force acts on an object, only the strongest force matters. It's as if the weaker forces were not there, and the object moves in the same way as if only the strongest force were acting on it." Do you agree or disagree with this student? What evidence from this activity supports your thinking? $4. Two fan units of strength 30 N and 40 N push on a moving cart in the same direction as its motion, while a 65 N frictional force acts in the opposite direction. Cart 1 Fan 2 30 -65 Friction Fan 1 40 What is the net force (strength and direction) acting on this cart? What will happen to its speed if these forces continue to act on it? CF-11Unit CF $5. In the Initial Ideas section of this activity you were asked about the motion of a cart with two fan units of unequal strength attached. Students in a previous class performed this experiment and noticed that, after their initial push, the speed of the cart steadily decreased The students were not sure at first which of the two fans was the strongest, and so their instructor asked them to determine this (based on their observation) and construct an explanation for how they know. Explanation: Which of the two fans was the strongest while the cart was decreasing in speed.? Describe the Situation using a diagram: Force applied to cart by Force applied to cart by Fan #1 Fan #2 int mon sarabivel Write the narrative: The initial push gets the cart started moving to the right, but after the hand loses contact the only forces acting on the cart are from the contact push/pull interactions with the two fan units. When a weaker force opposes a stronger force, an object will move in the direction of the stronger force, but will slow down as it does so. Since the cart is decreasing in speed after the initial push, this means the force in the direction of motion must be stronger than the force in the opposite direction, so Fan #1 (in the direction of motion) must be stronger than Fan #2 (in the opposite direction to the motion). Evaluate this Explanation: Is this explanation good or problematic? (Remember, it should be well- constructed, accurate, and well-reasoned.) If you find this explanation to be good, give your reasons below. If you find it to be problematic, again give your reasons and also correct it. CF-12