1st Law
An earthquake happens during a hockey game shifting the entire rink north 2 cm. The puck was at rest on the center line of the rink. Where is the puck now?
2 cm south of the center line.
What are the 3 versions of math equations of Newton's 2nd Law?
a = F/m
m = F/a
What were the 4 forces involved in the hand, washer, rubber band drawing?
Hand on the washer (friction-force pair 1)
Washer on the hand (friction-force pair 1)
Washer on the rubber band (normal-force pair 2)
Rubber band on the washer (normal-force pair 2)
An object has balanced forces on it. Describe its motion.
• Speed?
• Direction?
Speed: Constant
Direction: Straight line path
The eggs in the henhouse are right where the hens laid them a few hours ago.
1st Law
Objects will stay at rest.
If an elevator starts moving and is accelerating upwards, how would the passengers feel?
Heavier than usual since there is an extra force and acceleration upward on their body.
To accelerate the fan cart as much as possible, what conditions would you set for...
a) the number of fans?
b) the number of blocks?
a) 3 fans (as much force as possible)
b) 0 blocks (as little mass as possible)
4 properties of force pairs:
Same force
Act on different objects
Equal in magnitude
Opposite in direction
Why can Mr. A push a car in neutral forward, but cannot lift its tires off the ground?
Pushing the car doesn't require opposing the gravity from Earth, just opposing the inertia.
It also helps that the car's wheels minimize the forces from friction.
The farmer's truck requires more gas to accelerate when it is hauling a load.
2nd Law
Gas represents the force from the engine and having a load in the truck represents there being a larger mass.
An air freshener is hanging from the rear view mirror in your car. You are travelling forward at 25 mph when you hit a tree. You notice the air freshener swing. Which way does it swing?
Forward, since inertia will keep the air freshener moving forward.
To build a faster car, what effect would building a stronger engine have…
a) on the free-body diagram?
b) on the equation a = F/m?
a) increases the applied force
b) increases net force and acceleration
A book is at rest on a table. Which is stronger, the normal force of the table upward on the book, or the normal force from the book downward on the table?
They are the same magnitude.
Explain why the Earth doesn't accelerate toward an airborne object's gravitational pull.
It does, but the acceleration is very small since Earth's mass is very large.
The horse pulling on the cart with 100 N is also pulled backward by the cart with 100 N.
3rd Law
Equal and opposite force pairs
Why didn't the penny fall in the cup if you pulled the index card slowly?
Friction had a chance to pull on the penny, as opposed to when this was done quickly, when friction didn't have that opportunity.
How much force would Sid need to push his 40-kg brother in order to accelerate him at 2 m/s^2?
F = ma
F = (40)(2)
F = 80 N
A horse pulls a cart forward. How does the horse accelerate forward if the cart pulls back with an equal amount of force?
There are other forces on the horse besides the cart's force. The net force is unbalanced, so the horse can accelerate forward.
If a bucket is filled with water and someone swings the bucket in a circle over their head, why doesn't the water fall out?
Inertia keeps the water travelling upward while the bucket is upside down.
Even when the tractor runs out of gas, it still coasts forward until friction stops it.
1st Law
The tractor's inertia keeps it moving until and outside force causes acceleration.
Why would the driver feel like they were being pushed into the passenger seat if they were turning left?
Inertia would make them travel in a straight path. The driver's body would slide sideways to achieve that straight path.
Explain to Bobby why he can hit the baseball (150 g) further than a softball (200 g). All of Bobby's swings have the same amount of force.
a = F/m. If F is the same each time, and the mass of a baseball is smaller, it will accelerate more.
How does friction help you walk across the floor?
The floor pushes back on you in the opposite direction you push on it.
Why do objects stay in orbit?
An object in orbit travels quickly in a straight line (1st Law). If there were no gravity pulling it toward Earth, it would escape Earth.
The rate of escape away from Earth and the rate of falling toward Earth are in perfect balance so the object doesn't get further away or closer to Earth.
Several farm hands cooperate to lift the tipped tractor back up. One couldn't do it alone.
2nd Law
Several farm hands would increase the force, which increases the acceleration from what one farm hand could do alone.