Q&A on Circular Motion

This is a Slow Motion video of how the water in the bucket is not spilling out because of centripetal force

Q: What is centripetal force?

A: Centripetal force is what we call a force that is perpendicular to motion. A centripetal force can be any force, gravity, tension, friction, but it must be perpendicular to the motion of the object.

Q: Why is centripetal force circular?

A: Centripetal force is circular because the force acting on the object is a continuous perpendicular force. If the force is not constantly being acted upon the object, then it the motion will not be circular.

Q: What are some examples of centripetal force?

A: A car uses centripetal force to turn: the friction of the tire on the ground causes the turn. Also, a swinging a ball on a string uses centripetal force because the string has a tension force, causing the ball to move in a circle.

Q: If you were to cut the string attached to the ball as it was moving, what would happen?

A: The ball would move in a straight line in the direction of the velocity because of inertia. Here's a picture that better explains it: 

Q: What is centripetal acceleration? 

A: For every unbalanced force, there is acceleration. Because centripetal force is not a balanced force, there is centripetal acceleration. Centripetal acceleration is in the same direction as the centripetal force, which is ALWAYS inward. To calculate centripetal acceleration, use this equation: 

Ta-da! Hope you now have a better understanding on centripetal force!

The Catapult Project

Wow! What a relief. For the past few weeks, I have been working with my fellow lab table mates on a catapult. This was quite the project. We had to consider many different forces and laws to make sure our catapult would, first of all, actually work when made of popsicle sticks, and secondly, launch farther than one meter. We were able to launch our catapult more than one meter, but the process to get there was very difficult.

When first starting, we drew out our catapult. I used a design I found from stormthecastle.com, a site which I found some very creative designs. I chose a triangle shaped catapult for it looked the simplest and easiest to change if something went wrong. After beginning, our group decided to build a platform for our catapult and also make the arm longer so the golf ball we were launching would go farther. Next, we agreed on making our angle of launch at about 47˚ because, when we were practice launching, that gave us the best distance. We also knew gravity, which would affect the golf ball's inertia, would be a pretty big factor, so we used a lot of tension force (all rubber bands) to get our arm to launch fast, which also increased the acceleration of the golf ball, therefore causing it to launch farther. Although we could not control the mass of the golf ball we used, we made sure that the force on the golf ball was great so, again, the golf ball would be able to accelerate. Finally, we made sure to hold our catapult down when shooting so it would not come back and crack the popsicle sticks holding the arm straight.

My whole group really enjoyed this project, and if anyone ever has some free time, I would definitely try making a catapult. It is fun and really helps you realize how forces affect real life!

Our Catapult!

What is a Scale and What is it Measuring?

I found this video quite funny. 

So does a scale measure weight? No! A scale is used to measure the amount of force you are pushing on the scale due to the amount of force you are pulling on Earth. Although your mass should be in Newtons, it is is pounds because you divide your weight in Newton's by 9.8 m/s2 because of acceleration. 

Here's a cool article that explains the difference between weight and mass:

http://www.mathsisfun.com/measure/weight-mass.html

Are they Really the Same?

vs

Newton's Second Law and Newton's Law of Gravitation use two very specific equations to calculate force. The Second Law states that Foce is equal to Mass times Acceleration. The Law of Gravitation states that Gravitational Force (Fg) is equal to G (the gravitational constant) times the Mass of the first object times the Mass of the second object divided by the Distance squared between the two items. Both equations solve for force, but are they the same?

The two laws can be the same! If when solving for Newton's Second Law you are solving for the gravitational force on the object, then the two equations equal one another. However, if you are using F=ma to solve for a different kind of force, like magnetic or friction, you can not you the gravitational force equation.

The mystery had been solved!

Newton's Law of Gravitation

Here's a great video to help you really understand this law. Khan Academy is the best!

Also, here's a quiz I made about this law to help anyone about to take a test on it study.

True or False

a.     Newton’s Third Law states every action has an equal and similar reaction.

b.     If the two objects have the same mass, then they have the same acceleration.

c.     For every one object, there is a gravitational force.

d.     GC is the symbol used for the gravitational constant.

Short Answer

a.     What are the three items the force of gravity depends on?

b.     Write out the two equations used to find force.

c.     When is the tide high? Low? Explain your reasoning.

Answers

1.     False: equal and OPPOSITE 

2.     True

3.     False: for every TWO objects

4.     False: G is the gravitational constant

5.     Mass of each object, distance between the two objects (radius), gravitational constant

6.     Fg=G m1m2/r(squared) and F=ma

7.     High= when moon is on that side of Earth; Low= when moon is not on that side of Earth; This is because the Moon has a gravitational attraction to the Earth, just like Earth has a gravitational attraction to the Moon.

Newton's Second and Third Laws

Here is a summary of the notes I took on Newton's 2nd and 3rd Laws.

Newton’s 2^nd Law

·      A=f/m

·      Relationship that shows force is prop. to acceleration and mass is inversely prop. to acceleration

·      Inversely proportional: if mass increased by 2, acceleration would DECREASE by 2

·      Proportional: if force is increased two times greater, acceleration also increases 2 times more

Examples of 2^nd Law

·      A ball hitting a wall and bouncing back

·      A hammer striking a nail into a piece of wood and the hammer ”bounces” back

·      This picture shows how acceleration and mass are inversely proportional, but force and acceleration are proportional

Newton’s 3^rd Law

·      The force from the 1^st object to the 2^nd object is ALWAYS equal to the force from the 2^nd object to the 1^st object

·      Even if only one object is pulling, force is still equal

·      Dealing with two objects, not just one

·      Forces are separate for each object

Examples of 3^rd Law

·      A person standing on a skateboard, pushes on a wall, and accelerates backwards.

                              

o   The wall is applying a force to you causing you to move backwards

o   The person accelerates because only one force is acting on the person

o   The force of the person pushing the was and the table pushing back are independent of one another

·      This picture shows how a rocket is launched into space using Newton’s 3^rd Law

Review Questions to Remember

·      When skydiving, at what point is the net force…

o   0N?

§  When diving at a constant speed; terminal velocity

o   -_N?

§  When free falling; before reaching terminal velocity

o   +_N?

§  When the parachute has deployed

·      When skydiving, why is acceleration positive when parachute is deployed?

o   To slow down, accel. must be in opposite direction of velocity, and velocity is negative when skydiving, so accel. is positive

·      If an astronaut is traveling alone in space and needs to get back in the shuttle, how can he do this?

o   Push off of (or throw) tools he has with him in opposite direction of where he needs to go

Newton's First Law

In class today, we went over Newton's First Law. Here's my graphic organizer to give a better idea of this topic.