Newton Car Lab. Newton s 1 st Law - Every object in a state of uniform motion

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1 Newton Car Lab Physics Concepts: Newton s 1 st Law - Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. This we recognize as Galileo s concept of inertia, and this is often termed simply the "Law of Inertia." Newton s 2 nd Law If an unbalanced (net) force acts on an object, that object will accelerate (or decelerate) in the direction of the force. Newton s 3rd Law For every action force, there is an equal and opposite reaction force. A body at rest is considered to have zero speed (a constant speed). So, any force that causes a body to move is an unbalanced force. Also, any force, such as friction, or gravity, that causes a body to low down or speed up, is an unbalanced force. This law can be shown by the following formula. F=ma F is the unbalanced force (vector) m is the object s mass (scalar) a is the acceleration that the force causes (vector) Force and acceleration are both vector quantities. In this law the direction of the force vector is the same as the direction of the acceleration vector. Vector and Scalar Quantities: An understanding of vectors is essential for understanding of physics and Newton s Second Law. A vector is a quantity that has two aspects. It has a size, or magnitude, and a direction. In contrast, there are quantities called scalars that have only size. If a quantity has only a size, it is called a scalar. Mass, distance, speed, time and temperature are examples of scalars. If a quantity has a size and a direction, it is a vector quantity. Force, acceleration, velocity, displacement, gravitational field, torque, and electric and magnetic fields are all vectors.

2 Materials (per group): 3 3-inch No. 10 screws (round head) 1 wooden block about 10 x 20 x 2.5 cm four small plastic wheels and two straws to connect the wheels. two larger straws to place over the thin straws so that the wheels will turn easily when taped onto the wood. Plastic film canister Assorted materials for filling canister (e.g. washers, nuts, etc.) 3 Rubber bands Cotton string Safety lighter or matches Eye protection for each student Vice Screwdriver Meter stick Setup: Cut a block of wood for each group and drive three screws into each block. Place the plastic caps and straws under the wood block and tape with masking tape. The activity requires students to load their slingshot by stretching the rubber bands back to the third screw and holding it in place with the string. The simplest way of doing this is to tie the loop first and slide the rubber bands through the loop before placing the rubber bands over the two screws. Loop the string over the third screw after stretching the rubber bands back. Use a match to burn the string. The small ends of string left over from the knot acts as a fuse that permits the students to remove the match before the sting burns through. To completely conduct this experiment, student groups will need six matches. Tell the students to tie all the string loops they need before beginning the experiment. The loops should be as close to the same size as possible. Loops of different sizes will introduce a significant variable into the experiment, causing the rubber bands to be stretched different amounts.

3 This will lead to different accelerations with the mass each time the experiment is conducted. Questions to ask: Explanation: Use plastic film canisters for the mass in the experiments. Direct students to fill the canister with various materials. This will enable them to vary the mass twice during the experiment. Have students weigh the canister after it is filled and record the mass on the student sheet. After using the canister, three times, first with one rubber band and then with two and three rubber bands, students should refill the canister with new material for the next three tests. Will the size of the string loop change the car s acceleration? Why? Will the placement of the mass on the car change the car s acceleration? Why? Will the amount of mass on the car change the car s acceleration? Why? How is the Newton car similar to rockets? How do rocket engines increase their thrust? Why is it important to control variables in an experiment? The Newton car provides an excellent tool for investigating Newton s Second and Third Laws of Motion. The Newton car serves as a slingshot. A wooden block with three screws driven into it forms the slingshot frame. Rubber bands stretch from two of the screws and hold to the third by a string loop. A mass sits between the rubber bands. When the string is cut, the rubber bands throw the block to produce an action force. The reaction force propels the block in the opposite direction (Newton s Third Law of Motion). The experiment allows students to launch the car while varying the force by changing the number or rubber bands and the mass thrown off the car. They will measure how far the car travels in the opposite direction. Recording Data: Assessment: Students should record their data as they conduct the experiment. They should record the distance their car goes with at least two different masses and with at least two different placements of the mass. They can graph their results in Excel and create a chart to help them analyze the data (see the sample data table below). Assessment will be performance based with weight given to participation in the lab itself, data recording, final graphs and analysis of the data. National Science Standards: Content Standard A- Science as Inquiry Content Standard B- Physical Science Unifying Concepts and Processes

4 Data Table and Lab Report for Newton Car Lab Record the distance your car travels with at least two different masses and at least two different placements of the mass, varying the number of rubberbands. Tria l # # of rubberbands placement of mass amount of mass 100 g (constant for 1st 4 trials) line g line g line g line g (constant for last 4 trials) line g line g line g line 2 The following questions will help you to analyze your data and draw conclusions: 1. Which law explains what happens in this lab? Dependent distance traveled (cm) 2. State the law. 3. What was the action? 4. What was the reaction? 5. Which independent variables made your car go the farthest? Look at you data and be sure to include all the variables that made it go the farthest. 6. Why do you think those variables made it go farther? Think about the equation P=MxV as you explain your analysis. If your data was inconsistent, explain why you think it was inconsistent.

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