FORCES AND MOTION
Mass: (amount of stuff) does not change; weight does.
Weight: the effect of gravity on matter
We weigh less on the moon, which is less massive than the earth, since the force of our attraction for the moon and its for us (which squeezes a scale between us) is less. We weigh more when we eat too much because the force of the attraction is greater with our larger mass.
Gravity is the attraction of 2 masses. If either one is bigger, there's a bigger attraction.
Ex: jumping up and down...there is an attraction between your body and the Earth
Despite weighing more, a more massive object falls at the same speed as a less massive object (if air resistance isn't a factor) because the extra force of attraction is counteracted by the inertia (stubbornness, resistance to change) of the bigger object. (Shoe and penny fell at the same rate.)
Newton's First Law of Motion: an object at rest tends to stay at rest, while an object in motion tends to remain in motion in the same direction and speed (unless it is acted upon by an outside force).
Deform: when objects change shape as they are pushed/ pulled
Elastic: object returns to its original shape when the force is removed
Ex: rubber band, balloon, spring
Plastic: objects that remain distorted
Ex: modeling clay
Friction: a force that opposes the motion of an object.
Ex: If you are sliding forward, friction will be in the other direction, slowing you down - negative acceleration.
Inertia: Things will keep doing what they are doing; they are stubborn.
Motion: velocity and acceleration
Demonstrations:
Mass: (amount of stuff) does not change; weight does.
Weight: the effect of gravity on matter
We weigh less on the moon, which is less massive than the earth, since the force of our attraction for the moon and its for us (which squeezes a scale between us) is less. We weigh more when we eat too much because the force of the attraction is greater with our larger mass.
Gravity is the attraction of 2 masses. If either one is bigger, there's a bigger attraction.
Ex: jumping up and down...there is an attraction between your body and the Earth
Despite weighing more, a more massive object falls at the same speed as a less massive object (if air resistance isn't a factor) because the extra force of attraction is counteracted by the inertia (stubbornness, resistance to change) of the bigger object. (Shoe and penny fell at the same rate.)
Newton's First Law of Motion: an object at rest tends to stay at rest, while an object in motion tends to remain in motion in the same direction and speed (unless it is acted upon by an outside force).
Deform: when objects change shape as they are pushed/ pulled
Elastic: object returns to its original shape when the force is removed
Ex: rubber band, balloon, spring
Plastic: objects that remain distorted
Ex: modeling clay
Friction: a force that opposes the motion of an object.
Ex: If you are sliding forward, friction will be in the other direction, slowing you down - negative acceleration.
- Friction can also help you turn. Since inertia says you will continue to travel in a straight line at the same speed unless acted on, the friction of tires when you turn the wheel creates a force pushing the car off its straight line.
- Friction is a way that kinetic energy can turn into heat
Inertia: Things will keep doing what they are doing; they are stubborn.
- Moving things will keep going in a straight line at the same speed unless acted on by an unbalanced force. Ex: key drop or swung sponge
- Still things will stay still unless acted on by an unbalanced force. Ex: dollar bill moved from between soda bottles
- The more massive something is, the more inertia has (the more stubborn it is). Ex: paper dragon, throwing heavy and light things back and forth - which is easier to get going, which is easier to stop
Motion: velocity and acceleration
- Velocity (speed in a direction) is the distance traveled divided by the time it took to travel that distance. Common units for this would be meters per second (m/s) or miles per hour (mph).
- Since velocity may change, we often refer to average velocity.
- When something changes velocity, we say it accelerates. (Even slowing down is acceleration, just negative acceleration.)
- Since objects have inertia (tendency to keep going at the same speed in the same direction), it takes an unbalanced force to change their motion (see inertia section above). Thus, acceleration requires an unbalanced force. A rapid acceleration (e.g. "My care goes from 0 to 60 in 3 seconds!") requires lots of force.
- If you see a change in velocity, look for the unbalanced force that caused it!
- "Unbalanced" force mean force is greater one way than another. If I'm standing on the floor, gravity pulls me down and the floor pushes up; there are forces, but they're balanced, so there is no movement. If I'm falling, the force of gravity isn't balanced, so I accelerate down.
Demonstrations:
1. Slow Race
- Materials: 2'x2' peg board, bolts with nuts and wing nuts, rubber bands, ping pong ball
- Try to make the ball roll all the way down the "maze" you create using rubber bands, nuts, and bolts.
- The goal is to make it roll as slowly as possible.
- Many strategies will be explored: slope, thickness of rubber bands, friction slows ball
- Estimate the average speed of your ball by dividing the seconds by the distance.
- Idea derived from Robert Kramf website http://thehappyscientist.com/science-video/slow-race
2. Friction Board http://asulearn.appstate.edu/pluginfile.php/258023/mod_resource/content/1/Friction_5E.pdf
- Assessed prior knowledge by discussing the term "friction."
- Rub hands together to produce heat.
- Observed/ Inferred using different types of sandpaper with various levels of grit (feeling different amounts of friction when they rubbed their fingers across it)
- Looked at bottom of their shoes and discussed how some shoes (tennis shoes, cleats, etc.) had the most "grip"
- By looking at ball bearings, students decided that oil reduces friction (Explored the idea by rubbing finger on bottom of a plastic bin, then putting vegetable oil on it to see if it reduced the friction- slippery)
- Experimented by doing rope, board, and chair activity
- Collected data (in form of graphs using technology software) of how much friction was involved while the student pulled himself across the carpet
- Wanted to reduce friction
- Decided on putting hundreds of tennis balls under the wooden board (to act as ball bearings)- Made predictions on graph first, comparing it to the previous data- Tested it to find their predictions were correct
- Wrapped lesson up by discussing idea of friction (possible ways to reduce or increase it, drew ideas on graphs)
- Came to conclusion that increased friction requires more force to overcome and decreased friction requires less force to overcome.