Slide 1 / 159 Slide 2 / 159 8th Grade Forces 2015-10-27 www.njctl.org Slide 3 / 159 Forces and Motion Click on the topic to go to that section · Motion · Graphs of Motion · Forces · Newton's Laws of Motion · Newton's 3rd Law & Momentum
Slide 4 / 159 Motion Return to Table of Contents Slide 5 / 159 What does it mean to be in motion? With a partner, come up with a scientific explanation of what it means if an object is in motion. Don't just say an object is moving! Slide 6 / 159 What does it mean to be in motion? An object is in motion if it changes position in relation to a certain place, called a reference point. Reference points are places or objects used to determine the motion of an object. It is extremely important to choose reference points carefully.
Slide 7 / 159 Relative Motion Motion is relative as it is dependent upon the reference point. Are you in motion right now? Think about it... Are you in motion compared to your desk? Are you in motion compared to the sun? Slide 8 / 159 Measuring Motion Speed is one of the many ways we measure motion. 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! Slide 9 / 159 Finding Speed Speed = Distance ⁄ Time and We can rearrange the letters in the speed equation and solve for any of the other 2 pieces of information.
Slide 10 / 159 Finding Speed Discussion time! · What are some possible units to measure speed? Remember 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, an animation of an internal combustion engine is shown below. Slide 11 / 159 Units for Speed The SI unit for distance is meters (m) and for time is seconds (s). Given these units, what will be the SI unit for speed? (Hint: recall the speed equation speed= distance/time) Slide 11 (Answer) / 159 Units for Speed The SI unit for distance is meters (m) and for time is seconds (s). Given these units, what will be the SI unit for speed? (Hint: recall the speed equation speed= distance/time) Answer meters/second which is usually shortened to m/s [This object is a pull tab]
Slide 12 / 159 1 A snail travels a distance of 10 m in 6000 seconds. What is the snail's average speed? 60000 m/s A 0.02 m/s B 600 m/s C 0.002 m/s D Slide 12 (Answer) / 159 1 A snail travels a distance of 10 m in 6000 seconds. What is the snail's average speed? 60000 m/s A 0.02 m/s B D Answer 600 m/s C 0.002 m/s D [This object is a pull tab] Slide 13 / 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
Slide 13 (Answer) / 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 C Answer B 4500 m C [This object is a pull 500 m tab] D Slide 14 / 159 Manipulate the speed of each car, solve for time, and predict which car will win! Slide 15 / 159 Speed When we talk about speed, it is important to know that there is a difference between instantaneous speed and average speed. Average speed can be calculated by dividing the total distance by the total time. This is what is usually calculated by runners in a race. Instantaneous speed is the speed of an object at any moment in time (an instant of time). Can you think of an example where you would use instantaneous time?
Slide 16 / 159 Average vs Instantaneous Speed It might take 3 hours to travel 300 km in a car. What would the average speed of the car be? Calculate it now. Does that mean the car was going that speed for the whole 3 hours of the trip? When you go on a trip in the car, do you go the same speed the whole time? Talk to a partner about this. Slide 17 / 159 Average vs Instantaneous Speed Have you ever run a mile? Do you think you ran at the exact same speed the entire mile? Think about what runners do at the very end of a race. Slide 18 / 159 Average vs Instantaneous Speed When you ride on the bus to school, does the bus driver travel at the same speed the entire trip? School buses and other vehicles have speedometers that measure the speed of the vehicle at a specific moment in time. Do speedometers measure average speed or instantaneous speed?
Slide 19 / 159 3 Your teacher times your mile run at 7.5 minutes, that means your speed was 0.13 mile/min. Was this your average speed or your instantaneous speed? AAverage Speed BInstantaneous Speed Slide 19 (Answer) / 159 3 Your teacher times your mile run at 7.5 minutes, that means your speed was 0.13 mile/min. Was this your average speed or your instantaneous speed? avg speed = AAverage Answer Speed 1 mile/ 7.5 min = BInstantaneous 0.13 mile/min Speed [This object is a pull tab] Slide 20 / 159 4 A student has built a model car that is designed to run at a constant speed. What should the student measure to test whether the car runs at a constant speed, average or instantaneous speed? AAverage Speed BInstantaneous Speed
Slide 20 (Answer) / 159 4 A student has built a model car that is designed to run at a constant speed. What should the student measure to test whether the car runs at a constant speed, average or instantaneous speed? instantaneous AAverage Speed Answer speed BInstantaneous Speed [This object is a pull tab] Slide 21 / 159 5 A swordfish travels for two hours. The first hour he covers 110 kilometers, and the second hour he covers 84 kilometers. What is the average speed of the swordfish? A 110 km/h Hint: Remember that B 84 km/h Average speed is total distance travelled divided by total time C 97 km/h D 194 km/h Slide 21 (Answer) / 159 5 A swordfish travels for two hours. The first hour he covers 110 kilometers, and the second hour he covers 84 kilometers. What is the average speed of the swordfish? A 110 km/h C Answer Hint: Remember that B 84 km/h Average speed is total distance travelled divided by total time C 97 km/h [This object is a pull tab] D 194 km/h
Slide 22 / 159 6 A dog walks outside to go the bathroom every day. On a given day, she walks 75 meters before she finds a spot to use the bathroom. She walks at an average speed of 2.5 meters per second. How long does it take her to find a place to use the bathroom? A 30 seconds B 2 minutes C 188 seconds D 90 seconds Slide 22 (Answer) / 159 6 A dog walks outside to go the bathroom every day. On a given day, she walks 75 meters before she finds a spot to use the bathroom. She walks at an average speed of 2.5 meters per second. How long does it take her to find a place to use the bathroom? A 30 seconds B 2 minutes Answer A C 188 seconds [This object is a pull D 90 seconds tab] Slide 23 / 159 Velocity Velocity is another way to measure motion. Simply put, velocity is the speed of an object with a direction included . Runner's speed: 10 km/hr Runner's velocity: 10 km/hr to the East What do you notice about the units for speed and velocity?
Slide 24 / 159 Why is velocity important? Have you ever been in an airplane? Would would be the consequence of a pilot only knowing the speed of other nearby planes? Tornadoes travel at about 170 km/h. Why is knowing the velocity of a tornado important? Slide 25 / 159 7 Carlos and Gina are riding on their horses to go into town. They travel 70 meters in 7 seconds going west. What is their velocity? A 490 m/s west B 10 m/s west C 490 m/s D 10 m/s Slide 25 (Answer) / 159 7 Carlos and Gina are riding on their horses to go into town. They travel 70 meters in 7 seconds going west. What is their velocity? A 490 m/s west B 10 m/s west Answer B C 490 m/s D 10 m/s [This object is a pull tab]
Slide 26 / 159 8 A car travels 100 km/h west for 2 hours. The car then travels 50 km/h east for one hour. What is the car's final position relative to its starting position? A 50 km west Hint: Find the distance and direction traveled for B 150 km west each leg of the trip first. C 250 km west Draw these distances on a number line using 0km D 50 km east as the starting point. Slide 26 (Answer) / 159 8 A car travels 100 km/h west for 2 hours. The car then travels 50 km/h east for one hour. What is the car's final position relative to its starting position? A 50 km west Answer B Hint: Find the distance and direction traveled for B 150 km west each leg of the trip first. C 250 km west Draw these distances on [This object is a pull a number line using 0km tab] D 50 km east as the starting point. Slide 27 / 159 Graphing Motion Return to Table of Contents
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. Position Time Slide 28 (Answer) / 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. Answer Position Position Time Time [This object is a pull tab] Slide 29 / 159 Graphing Motion Use the graph below to calculate speed at 1, 2, and 3 seconds. Do you notice a pattern?
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