Gravity, Air Resistance, and Motion Laws

Unit Vocab Flashcards

View List |Play Match Game |Play Waterfall Game

Gravity

(c) M. Prince, 2013

Gravity is the force that pulls two objects together.  If that's so, why is it I am not more attracted to my bed when it's time to get up in the morning?  Well, mass has a great deal to do with gravity.  The more mass an object has, the more gravitational pull.  Unfortunately, since my bed doesn't have as much mass as the Earth, I have a much greater chance of being pulled to the Earth, then being pulled to my bed.  Let's consider the example provided on the anchor chart in class.  We have two kids sitting next to one another in the grass.  Because the gravitational pull is weaker between them then each to the Earth, they will be more attracted to the Earth than one another because of the difference in the amount of their masses and the mass of the Earth.

Now there is another event that can influence the gravitational pull between objects.  The closer one object is to the next object, the greater the gravitational pull.  The further away one object is from another one then the  lesser the gravitational pull is between the objects. Again, let's go back to the image on the anchor chart in class.  The gravitational pull between you and Earth is much greater than the gravitational pull between you and Venus.  The distance between you and Venus is much greater than the distance between you and Earth.

Air Resistance

(c) M. Prince, 2013

Air resistance is the opposing force between forward movement and the air.  Air is a gas and therefore it makes air resistance one example of fluid friction.  Remember, fluid friction occurs between a gas or liquid and an object that is surrounded by the air or liquid.  Fluid friction resists the movement of a solid object through a fluid. Air resistance is an upward force.  Think about the picture in the textbook with the leaf and acorn.  These objects are falling from the tree.  Since falling implies a downward motion the opposing force would be exerted in an upward motion.  Both objects don't fall at the same rate because of their different surface areas.  The greater the surface area = the greater the air resistance; the lower the surface area = the lesser the air resistance. How does the weight and gravitational pull influence the falling of these two objects?

Friction

There are four types of friction as we learned and reviewed in class last week.  Read more about friction here and watch this video here. Friction is helpful because it helps to create warmth when two surfaces rub against one another. Friction slows down motion with is helpful especially when a traffic light is going from yellow to red. Friction can be an obstacle too! If there is too much friction it makes it hard for an object to move, it wears down objects.  Too little friction can be an issue too!  Recently, I purchased a new pair of heels. After I put them on and walked on a particular surface I almost slipped! Why? Well, there was not enough friction between the bottom of my shoe and the surface of the floor.  Friction is increased by the roughness of the surface.  Smoother surfaces have a lower frictional force, while a rough surface, like the road, creates more friction.  Check out this website of 25 examples of friction and determine how friction is either harmful, helpful, or both for each one. 

Motion Laws

1st - An object in motion stays in motion. An object at rest remains at rest.  Motion only changes when another force is exerted upon the object. What pictures can you create to make sense of this law?

2nd - Force is equal to the mass and the acceleration of an object. What pictures can you create to make sense of this law?

3rd - For every action, there is an equal and opposite reaction.What pictures can you create to make sense of this law?

Student Work on Motion and Forces

Created with Padlet