Slide 1 / 159 Slide 2 / 159 8th Grade Forces 2015-10-27 www.njctl.org Slide 3 / 159 Slide 4 / 159 Forces and Motion Click on the topic to go to that section · Motion Motion · Graphs of Motion · Forces · Newton's Laws of Motion · Newton's 3rd Law & Momentum Return to Table of Contents Slide 5 / 159 Slide 6 / 159 What does it mean to be in motion? What does it mean to be in motion? An object is in motion if it With a partner, come up changes position in with a scientific relation to a certain place, explanation of what it called a reference point. means if an object is in motion. Don't just say an Reference points are object is moving! places or objects used to determine the motion of an object. It is extremely important to choose reference points carefully.
Slide 7 / 159 Slide 8 / 159 Measuring Motion Relative Motion Motion is relative as it is dependent upon the reference point. Are you in motion right now? Think Speed is one of the many ways we measure motion. about it... Speed is a measure of the distance traveled per unit of time. That means you can find the speed of any object that is in motion! Are you in motion compared to your desk? Are you in motion compared to the sun? Slide 9 / 159 Slide 10 / 159 Finding Speed Finding Speed Discussion time! · What are some possible units to measure speed? Remember Speed = Distance ⁄ Time that speed= distance/time! · How do you think speed is measured when driving in a car? · How would you measure speed of an engine? For reference, and an animation of an internal combustion engine is shown below. We can rearrange the letters in the speed equation and solve for any of the other 2 pieces of information. Slide 11 / 159 Slide 12 / 159 Units for Speed 1 A snail travels a distance of 10 m in 6000 seconds. What is the snail's average speed? The SI unit for distance is meters (m) and for time is seconds (s). 60000 m/s A Given these units, what will be the SI unit for speed? (Hint: recall the speed equation speed= distance/time) 0.02 m/s B 600 m/s C 0.002 m/s D
Slide 13 / 159 Slide 14 / 159 2 A blimp travels at 3 m/s for 1500 s. What distance does the blimp cover in that time? 500 m/s A 4500 m/s B 4500 m C 500 m D Manipulate the speed of each car, solve for time, and predict which car will win! Slide 15 / 159 Slide 16 / 159 Speed Average vs Instantaneous Speed When we talk about speed, it is important to know that there is a difference between instantaneous speed and average speed. It might take 3 hours to travel 300 km in a car. What would the Average speed can be calculated by dividing the total distance average speed of the car be? Calculate it now. by the total time. This is what is usually calculated by runners in a race. Does that mean the car was going that speed for the whole 3 hours of the trip? Instantaneous speed is the speed of an object at When you go on a trip in the car, any moment in time (an do you go the same speed the instant of time). Can you whole time? Talk to a partner think of an example about this. where you would use instantaneous time? Slide 17 / 159 Slide 18 / 159 Average vs Instantaneous Speed Average vs Instantaneous Speed Have you ever run a mile? Do you think you ran at the exact same When you ride on the bus speed the entire mile? to school, does the bus driver travel at the same speed the entire trip? Think about School buses and other what runners vehicles have do at the speedometers that very end of a measure the speed of the race. vehicle at a specific moment in time. Do speedometers measure average speed or instantaneous speed?
Slide 19 / 159 Slide 20 / 159 3 Your teacher times your mile run at 7.5 minutes, 4 A student has built a model car that is designed to that means your speed was 0.13 mile/min. Was this run at a constant speed. What should the student measure to test whether the car runs at a constant your average speed or your instantaneous speed? speed, average or instantaneous speed? AAverage AAverage Speed Speed BInstantaneous BInstantaneous Speed Speed Slide 21 / 159 Slide 22 / 159 6 A dog walks outside to go the bathroom every day. 5 A swordfish travels for two hours. The first On a given day, she walks 75 meters before she finds hour he covers 110 kilometers, and the a spot to use the bathroom. She walks at an average second hour he covers 84 kilometers. What speed of 2.5 meters per second. How long does it take is the average speed of the swordfish? her to find a place to use the bathroom? A 30 seconds A 110 km/h Hint: Remember that B 84 km/h B 2 minutes Average speed is total distance travelled divided by total time C 97 km/h C 188 seconds D 194 km/h D 90 seconds Slide 23 / 159 Slide 24 / 159 Velocity Why is velocity important? Velocity is another way to measure motion. Simply put, velocity Have you ever been in an airplane? Would would be the consequence of is the speed of an object with a direction included . a pilot only knowing the speed of other nearby planes? Runner's speed: 10 km/hr Runner's velocity: 10 km/hr to the East Tornadoes travel at about 170 km/h. Why is knowing the velocity of a tornado important? What do you notice about the units for speed and velocity?
Slide 25 / 159 Slide 26 / 159 7 Carlos and Gina are riding on their horses to 8 A car travels 100 km/h west for 2 hours. The car go into town. They travel 70 meters in 7 seconds then travels 50 km/h east for one hour. What is the going west. What is their velocity? car's final position relative to its starting position? A 490 m/s west B 10 m/s west A 50 km west Hint: Find the distance C 490 m/s and direction traveled for B 150 km west each leg of the trip first. D 10 m/s C 250 km west Draw these distances on a number line using 0km D 50 km east as the starting point. Slide 27 / 159 Slide 28 / 159 Graphing Motion Graphs can be used to show motion and can be used to determine relationships! When graphing data, position should be on the y-axis and time on the x-axis. Drag and drop the variables onto the correct axis on the graph below. Graphing Motion Position Time Return to Table of Contents Slide 29 / 159 Slide 30 / 159 Graphing Motion Graphing Motion Use the graph below to calculate speed at 1, 2, and 3 seconds. Do you notice a pattern? 6 m/ 3s = 2 m/s 2 m/ 1s = 2 m/s 4 m/ 2s = 2 m/s The speed is 2 m/s at each of the three seconds! In other words, the speed is constant.
Slide 31 / 159 Slide 32 / 159 Graphing Motion Graphing Motion When interpreting a graph, it is important to look for relationships A weak relationship is when significant changes in one variable between variables. These relationships can be strong, weak, or not cause minimal changes in the other variable. Is there any pattern in present at all. the graph below? Circle the patterns. The graph below shows a strong relationship between position and time. Can you describe what this relationship is? Slide 33 / 159 Slide 34 / 159 Graphing Motion The Importance of Slope When there is no relationship between the variables, there will not Position versus time graphs can be used to find speed and be a pattern present. Is there any pattern in the graph below? compare speeds.When we talk about the slope of a line, we are talking about how steep a line is. Look at the skier to the right. He is on a very difficult trail. Would an easier trail be steeper or more flat? How would the slopes of these two trails compare? Slide 35 / 159 Slide 36 / 159 The Importance of Slope 9 Which walker has a greater speed? How can you tell in terms of the slopes of the In a position versus time graph, the y-axis is the position and the graphs? x-axis is the time. Recall that the relationship between position and time is speed. So when we are looking at the slope, we are looking at the speed . The slope of the black line gives us the speed of the bicycler. B A The steeper the slope of the line on a position versus time graph, the greater the speed!
Recommend
More recommend
