NEWTON’S 2ND LAW OF MOTION

Newton’s Second Law & Gravity We know 1 and 3, what happened to 2?

Let’s see what we already know from Newton What is Newton’s First Law? What happens when there is no force? What happens when there is a force?

More Review What is acceleration? What is a force?

Acceleration and Force Does applying a force always cause acceleration? No, net (total) force causes acceleration Examples where net force is zero? Do you need less or more force to produce more acceleration?

Acceleration and Mass The acceleration produced depends on the amount of mass pushed: More mass gives an object more inertia, which is laziness of movement The more mass the less acceleration The less mass the more acceleration http://www.youtube.com /watch?v=53rpQm7-thA

Newton’s Second Law Newton summarized the relationship between Force, Acceleration and Mass in his second law equation: F is force measured in Newtons (N) m is mass measured in kilograms (kg) a is acceleration measured in m/s2

Second law practicing – I do There is a left ward force of 30 N on a box sitting on the ground and a right ward force of 10 N on the box. If the mass of the box is 4 kg, what is the acceleration of the box?

Second law practicing – we do How much force do you need to need to push an elephant that squirts water that is 300 kg to accelerate 10 m/s2?

Second law practicing – we do You kick a soccer ball with 300 N of force and it accelerates at 5 m/s2. What is the mass of the soccer ball?

And now… Go do your You Do’s 

Free Fall Free fall refers to an object falling down and accelerating because of gravity Gravity is a force that causes all objects to accelerate at a rate of 9.8 m/s2 toward the center of the Earth g = 9.8 m/s2 All objects will fall at the same rate from the same height regardless of mass Because of air resistance, lighter object tend to fall slower in real life But without air resistance, everything will fall at the same time

Finally, Free Fall Explained Galileo showed that falling objects accelerate equally, regardless of their masses. But Galileo could not explain why the accelerations were equal.

Applying Newton’s 2nd Law With F=ma, we can now explain why a hollow and solid egg fall at the same time, or a hammer and feather hit the ground at the same time.

weight In physics, weight is the amount of force being applied on an object due to gravity It is calculated using F is force measured in Newtons (N) w is weight (a specific type of force) m is mass measured in kilograms (kg) g is acceleration due to gravity always equal to 9.8 m/s2 on earth

Because weight is dependent on gravity, your weight changes as you travel around Earth and the universe! That’s why we always talk about mass not weight when we want to talk about how heavy an object is

When we solve for weight, use g = 10 m/s2 just to make things easier When we solve for weight, use g = 10 m/s2 just to make things easier. On a quiz or a test, just choose the closest answer and you’ll be set 

What is the weight of a person who has a mass of 60 kg?

What is the weight of the same person from question 7, still 60 kg, but on the moon? The acceleration due to gravity on the moon is 1.6 m/s2.

Star Wars Watch the video of Luke and Yoda What do you notice about their command of the “force?”

Newton’s 2nd Law: Lecture Recap: Answer these on your own sheet What is Force? Units of force Newton: kg*m/s2 Second Law: Force = mass x acceleration F = ma; newtons The force in newtons equals the mass of an object multiplied by its acceleration

How does this relate to Star Wars? Remember when Luke was moving the rocks? Remember when Luke tried to move the x- wing? What happened in each situation? Which object was more massive? If Luke has a constant “force” why could he not move the larger object? Explain in terms of F=ma

The Snake Game On a sheet of paper, write the numbers 1 – 10 down the side (6 per table) This sheet of paper will not move, it stays at your table The point of the game is to see who can snake around the room during the game duration Longest Snake Wins Lottery Tickets You may move only if you get the right answer

This is how we move

Let’s practice Alfred Nobel invented this explosive, also the name of a Taio Cruz song?

Question 1 The acceleration of gravity is decreasing, constant or increasing?

Question 2 How much force do you need to accelerate a 430 kg car to 3 m/s2?

Question 3 What is the acceleration of a bike that goes from 2 m/s to 12 m/s in 2 seconds?

Question 4 A sumo wrestler is very “resistant to change” because he has a lot of _______________.

Question 5 The projector screen is about 5 kg. When I pull it down with a acceleration of 15 m/s2, what is the force I am exerting?

Question 6 The mass of a table is 30 kg. What is its weight?

Question 7 Your __________ changes as you move from the Earth to the moon, but your __________ doesn’t.

Question 8 How much did a 3 kg pen accelerate if the gravitational force on it is 20 N and the air resistance was 14 N?

Question 9 You go on a road trip. In the first hour, you travel 300 km. Then you take a break for two hours. Lastly, you drive 200 km in the last hour. What was your average speed?

Question 10 An object in equilibrium must be traveling at what type of velocity?