Projectile Motion Part 1
- 1. § Today, we will • Conduct an Inves4ga4on • Take some notes • Write a short reflec4on about what we learned § Please Do Now: • get your lab notebook • get out something to write with Good Morning!
- 2. § How does ini*al velocity affect the *me it takes a horizontally-‐ launched projec*le to reach the ground? § Take a few moments and read pg 174 – 175 in your text. As you read, be thinking about: • what materials will you be using • how the lab will help you answer the ques4on • what your hypothesis will be Today s Investigation
- 3. § Turn to the first clean page in your lab notebook and 4tle it, Chpt 2. Sec 4 -‐ Projec4le Mo4on, part 1 • Don t forget to make an entry in your table of contents § Copy the ques4on down at the top of your new page How does ini*al velocity affect the *me it takes a horizontally-‐ launched projec*le to reach the ground?
- 4. § Form a hypothesis that addresses the lab ques4on. • remember: a hypothesis is an if then statement – and if you re feeling par4cularly smart today, add a because statement aSer the then Projectile Motion, Part 1
- 5. § We re going to split the lab into two parts. Your group will have 20 minutes to complete Part A of the lab (#1 – 4) Time for the Lab!
- 6. § We’ll get back to the lab before the end of the period – so leave your lab notebook out and OPEN § For now, get out your spiral for notes and a clean sheet of notebook paper for your predictions/reAlection Time for Notes
- 7. It s as easy as rolling off a cliff…
- 8. § If this red ball had a net force to the right applied to it and rolled off the cliff at a constant speed, what would its path look like? Make a Prediction
- 9. Predict A B C Which path will the ball follow?
- 10. § Determine which path you believe the ball will follow AND WHY. Write your predic4on on a clean sheet of paper – we will be adding to this at the end of this lesson, so keep it neat! J Prediction
- 11. A B C A few years ago, researchers went to elementary, middle, and high schools as well as universities and showed students this image and asked them, Ignoring air resistance, which of the following correctly shows what an object would do if it rolled off a cliff?
- 12. § The breakdown of answers they got was almost exactly the same at all ages. § About 60% said number 1 was correct. The object will stop in midair, and then start to fall straight down. because some people referred to the coyote in cartoons, the researchers called it the Wile E. Coyote Effect. § About 25% said number 2 was correct. The object will move forward at first, but will eventually just fall straight down. § About 15% answered number 3. The object will con4nue to move forwards the en4re 4me it is falling. The Results
- 13. § I m not going to tell you. We ll revisit the ques4on at the end of these notes. J So What s the Correct Answer?
- 14. § Both coins fall the same amount ver4cally in the same amount of 4me. § The projected coin also moved to the right; but it fell downward at exactly the same rate as the dropped coin. Observations from the lab In your notes, sketch what the motion of these two coins must have looked like
- 15. § As we saw with the coin launcher, both coins – the one that fell straight down and the one that was flung out horizontally -‐ hit the ground at the same 4me. § So what effect did horizontal velocity have on the 4me it took (the downward mo4on) the coin to hit the ground? § The best conclusion we can make from this is that the horizontal mo4on of the coin does not affect downward mo4on of the coin. Observations from the Lab
- 16. § Intui4on will tell you that the horizontally launched object will hang in the air. § But… • YOUR INTUITION (at least in this case) IS WRONG! § Here s a video § Here’s another video Observations from the lab
- 17. The 4tle of this slide says it all: horizontal and ver4cal mo4on are independent of each other – even when they are happening at the same 4me! So…let s get back to the ques4on: Horizontal and Vertical Motion Don t Know Each Other Exist!
- 18. § It Doesn t! § What is the only factor (besides air resistance, which we are ignoring) that DOES affect the *me it takes a horizontally-‐launched projec*le to reach the ground? § How high off the ground the object is. How does initial velocity affect the time it takes a horizontally-‐ launched projectile to reach the ground?
- 19. Revisit Our Thinking A B C Which path will the ball follow?
- 20. 1. If a bullet is fired horizontally from a gun at the same instant a bullet is dropped from gun barrel height, which bullet hits the ground first? Explain your answer in terms of horizontal and ver*cal velocity, and gravity Reflection 2. Sketch the drawing on the right. Explain the significance of the coins being at the same height at each instance AND the significance of the increasing distances between the “strobe photo.” ADV: if the table is 5m high, how long are the coins in the air?
- 21. § The ver4cal posi4on of a projec4le constantly changes, though. • Why? • The constant force of gravity. § As the projec4le rises, it slows down. As it falls, it speeds up. § The change in velocity is ALWAYS 9.8 m/s every second. (9.8 m/s2) Motion of Every Object
- 22. § Any projec4le travels horizontally and ver4cally. § Ignoring air resistance, the horizontal velocity remains the same • REMEMBER: force doesn’t run out and the law of iner4a says objects in mo4on remain in mo4on at the same speed and direc4on unless a net force is applied. Motion of Every Object
- 23. § To keep the math super simple, let s round the change in velocity to 10 m/s2 § If a projec4le is thrown straight up at 40 m/ s, its velocity will decrease by 10 m/s every second. § At the top of its path, its velocity is 0 m/s… • but immediately, the object begins to fall back to earth where its velocity will increase by 10 m/s every second. Motion of Every Object