!When an object changes speed or direction, it is acceleration

Why is going around a curve at the same speed acceleration?

Acceleration = “change in velocity / time”

Change in velocity = “final velocity – initial velocity”

v_f stands for final velocity

v_i stands for intial velocity.

Units of acceleration are in meters per second, per second or meters per second squared –m/s².

We usually use m/s² as our units in this class.

Example: if a toy car speeds up by 2m/s every second, its acceleration will be 2 m/s/s, which can also be written as 2 m/s²

Steps to solve problems:

1. Circle what you are asked to find.

2. Underline given facts with numbers and units and write the symbol above it.

3. Check that your units “match”. (For acceleration, velocity and time units will not always match)

4. Write down your formula and rearrange for what you’re asked to find.

5. Put in numbers for symbols and solve.

6. Check that you answered the question asked and that you included units with your answer

Eample 1 : An object that can go from stop to 50 m/s in 5 seconds would have an acceleration of?

1. 
   A Porsche can go from rest to 60 mi/s in 5.2 seconds. What is its acceleration?
   

2. 
   A car going 22.2 m/s slows down to 10 m/s in 3 seconds. What is its acceleration?
   

3. 
   A skater increases her velocity from 2.0 m/s to 10.0 m/s in 3.0 seconds. What is the skater’s acceleration?
   

4. 
   A car accelerates at a rate of 3.0 m/s². If its original speed is 8.0 m/s, how many seconds will it take the car to reach a final speed of 25.0 m/s?
   

5. 
   While traveling along a highway a driver slows from 24 m/s to 15 m/s in 12 seconds. What is the automobile’s acceleration? (Remember that a negative value indicates a slowing down or deceleration.)
   

6. 
   A parachute on a racing dragster opens and changes the speed of the car from 85 m/s to 45 m/s in a period of 4.5 seconds. What is the acceleration of the dragster?
   

Bill Nye-Momentum https://www.youtube.com/watch?v=217dpIeuPVQ

Video #1- Bill Nye “Momentum” (about 23 minutes)

Answer the following questions during the Bill Nye video. Yes, the questions go in order. 

1. The faster you go the more _________________ you have.

2. Whenever an object is _____________ it has momentum.

3. The faster something is traveling, the more it weighs, and the more mass it has, the ____________of its momentum will transfer.

4. Why does the quarter only move a little bit?

5. If you added up all the momentum of all the pieces of the ornament and all the marbles, they would equal the ___________ amount of momentum as when the ornament just bounced off the truck.

6. If you are not moving, then you have ______ momentum.

7. In a rocket, the momentum of the hot fuel going one way _______________ the momentum of the rocket going the other.

8. a. He is bouncing two different balls. The momentum of the individual pieces is _________ to the momentum of the bouncing ball.

b. That’s what we call _____________________ of momentum.

9. What makes a soap box car move? _______________

10. How can rockets zoom through space where there is nothing to push against?

11. What happens when you drop a tennis ball while it’s on top of a falling basketball and why?

12. Momentum depends on how much things ______________ and how ___________they’re moving.

13. How is momentum used on a billiards table?

14. While you are in a moving car, you and the car / only you have momentum. (Circle one.)

15. When the car stops, you will keep moving. Which one of Newton’s laws is this? ________

(They don’t say this in the video. Do you remember?)

16. In croquet, the momentum of the mallet gets _________________ to the ball.

17. The momentum of the air in the balloon going one way __________ the momentum of the tape/straw/balloon assembly going the other way.

18. Fly vs. Windshield: Whose momentum wins? ______________

19. Explain how one of the scenes in the music video involves momentum.

20. a. At the end Bill says “Excuse me, I’ve got some __________ and __________ to multiply.”

b. What variable would that give him? __________

c. What unit would it be measured in? _________

The 100 kg fullback runs up the middle of the football field. Suddenly he collides with a 75 kg defensive back tackling him. The more massive fullback is thrown back 2 meters! How is this possible? The answer is MOMENTUM. All moving objects have MOMENTUM. Momentum is equal to the mass of an object multiplied by its velocity.

The Law of Conservation of Momentum states THE TOTAL MOMENTUM OF ANY GROUP OF OBJECTS REMAINS THE SAME UNLESS OUTSIDE FORCES ACT ON THE OBJECTS.

Think of a baseball bat meeting a baseball. What does the batter need to do to make the ball go the farthest? Why?
How is momentum transferred?

The more mass an object has, the higher its momentum.

Example: a Ford Focus traveling 50 mi/hr vs. a truck traveling 50 mi/hr

The faster an object is moving, the higher its momentum.

Example: A car traveling 10 mi/hr vs. that same car traveling 75 mi/hr

If an object is not moving, its momentum is zero.

The unit we use for momentum (p) is kg · m/s

Example: What is the momentum of a 25 kg object traveling north at 42 m/s?


LAB: Momentum Bashing

Introduction:

To better understand what happens in a car crash, it helps to see how force, inertia, and velocity are related in a property called momentum. The amount of momentum that object has depends on its mass and velocity. In this activity, you will determine how increasing mass affects the bashing power of marbles.

To find out how much momentum an object has, use the formula:

p (momentum) = mass x velocity

1. What determines if one car has more momentum than another in a two-car collision?

• 
  Ruler with center groove
  
• 
  4 marbles of the same size
  
• 
  5-oz plastic cup
  
• 
  Stop watch
  
• 
  3 beam balance or electronic scale
  
• 
  Meter sticks
  
• 
  Books to support track
  

1. 
   Cut a 3.0 cm square section from the top of the cup (as shown to the right).
   
2. 
   Place a ruler with one end on a textbook (about 3.0 cm height) and the other end resting on the desk.
   
3. 
   Place the 3.0cm opening of the cup on top of the ruler end that is on the desk.
   
4. 
   Place a meter stick alongside the cup to measure the distance (in cm) the cup moves.
   
5. 
   Position one marble in the groove at the maximum height of the ruler.
   
6. 
   Release the marble and observe the cup.
   
7. 
   Measure the distance the cup moved to the nearest 0.1 cm.
   
8. 
   Perform three trials for 1, 2, and 3 marbles and average the results.
   
9. 
   Record your data in the table provided.
   

1. 
   Compare your data for the glass marbles and different sized marbles. How are the results different? Explain your answer using concepts of momentum and inertia.
   
2. 
   Describe the general relationship between the number of marbles hitting the cup and the distance the cup moves.
   
3. 
   What if the cup were made out of steel? How would your data be different for the trials with the glass marbles? Explain your answer using concepts of momentum and inertia.
   
4. 
   Explain why a 40,000 kg truck traveling at 2 miles per hour has the same momentum as a 2,000 kg SUV traveling at 40 miles per hour.
   
5. 
   What is the momentum of a marble that has a mass of 1.2 kg and a velocity of +8.5m/s? Calculate the impulse needed to stop this marble.
   

1. 
   Imagine two cars on the road. A car with a mass of 700kg is traveling at a velocity of 30 km/hour toward another car with a mass of 500kg. The second car is traveling at a velocity of 40 km/hour. Using the formula for momentum (p=mv) which car has more momentum? What will be the outcome of this collision?
   

2. 
   Using the momentum formula, determine the momentum of a...
   

b. 1000-kg car moving northward at 20 m/s.

c. 40-kg freshman moving southward at 2 m/s.

3. 
   How much momentum does a 25 kg mass moving at 25 m/s have?
   

4. 
   How much momentum does a stationary 5500 kg mass have?
   

5. 
   What is the velocity of a 5.5 kg object that has a momentum of 550 kg·m/s?
   

6. 
   Compare the momentums of a 50 kg dolphin swimming at 16.4 m/s and a 4100 kg elephant walking 0.20 m/s.
   

7. 
   An object has a momentum of 55 kg·m/s and hits a stationary object making the second object starts to move. If the first object ends with a momentum of 13 kg·m/s, what is the momentum of the second object?
   

1. 
   A 5.0 kg baby on a train moving eastward at 72 m/s
   
2. 
   A 48.5 kg passenger on a train stopped on the tracks
   
3. 
   A 0.8 kg kitten running to the left at 6.5 m/s
   

1. 
   If a car travels 400 m in 20 seconds, how fast is it going?
   
2. 
   If you move 50 m in 10 se, what is your speed?
   

1. 
   How much time will it take for a bug to travel 5 meters across the floor if it is traveling at 1 m/s?
   
2. 
   You need to get to class, 200 meters way, and you can only walk in the hallways about 1.5 m/s. How much time will it take to get to your class?
   

1. 
   How far can you get away from your little brother with a squirt gun filled with paint if you can travel at 3 m/s and you have 15 s before he sees you?
   

2. 
   How far can your little brother get if he can travel at 2.5 m/s and in 5 seconds you will discover that his squirt gun is out of water?
   

You leave your house at 7:30 a.m. to go to school. You arrive at school at 7:50 a.m. the school is 3 miles from your house.

1. 
   What was your average speed in mph?
   

2. 
   If the speed limit on the road was 40 mph, how long should it take you?
   

3. 
   Explain why your calculated time does not match the actual time it took to get to school.
   

Constant Speed

An athlete sprints 100 meters in 12 seconds. She stops and does 20 push-ups in 88 seconds. She then jogs 1000 meters in 300 seconds. She walks another 500 meters in 400 seconds. Make a distance time graph of her motion. What is her average speed?

1. Listen carefully to the opening song and fill in the blank:

Inertia is a property of _________________________

2. What force was holding the anvil up? ____________________________

3. What force is pulling the anvil down? ______________________________

4. When he flicked the card where did the coin go to? _____________________________________

5. Whether moving or sitting still everything has _______________________________

6. The men who were trying to move the boxes read that:

Nothing gets moved unless it is P_____________________ or P_______________________

Newton’s Three Laws of Motion: Bill goes through the three laws of motion. Fill in the blanks.

Newton’s 1st Law of Motion

7. Things at rest, stay at _______________________

8. Things in motion stay in ____________________ unless acted upon by an outside force.

Newton’s 2nd Law of Motion

9. Force = _____________________ times acceleration.

10. For every action there is an equal and opposite ______________________________

_______ 11. What happened to the apple’s weight as the plane dived toward the ground?

A) Got large or heavier B) got less or weightless

_______ 12. What happened to the apple’s weight as the plane rose up towards the sky?

A) Got large or heavier B) got less or weightless

_______ 13. What do we measure mass in?

A. meters B. Liters C. Grams

14. Listen to the song and fill in the blank: We are all ________________________________.
Forces

Have you picked up a book or moved a desk? Have you ever dug in the sand or played baseball? In each of these activities, a force is involved. A force is a push or a pull. Forces give energy to and object and cause it to move or change its motion. All forces have magnitude and direction. Examples of forces include wind pushing on a flag on the flag pole or the moon pulling on the oceans to cause the tides. This energy can cause an object to start moving, stop moving or change direction.

The Greek philosopher Aristotle thought that in order to set an object in motion and keep it moving at a constant speed, a constant force has to be added. If the force were removed, the object would come to a stop. Based on your everyday experiences this seems to be true. However, in the seventeenth century, Isaac Newton proposed a different explanation for motion. He said that an object in motion should keep a constant velocity moving in a straight line. In other words, objects do not come to rest on their own. So what’s the deal here?

Friction of course! Friction is the force that brings an object to rest. Air resistance acts on objects and slows them down through friction.

Balanced and Unbalanced Forces

• 
  Forces that are not equal and opposite are called UNBALANCED FORCES. In unbalanced forces, one force is greater than the other. This causes a change in motion. When 2 unbalanced forces are exerted in opposite directions, the combined force is the difference between the 2 forces. If 2 unbalanced forces are exerted in the SAME direction, then the combined force is the sum of the 2 forces. A net force is defined as the sum of all the forces acting on an object. Force is measured in Newtons (N), after the famous scientist Isaac Newton.