Chapter 4 Physics
kilogram
the fundamental SI unit of mass.
inertia
the reluctance of any body to change its state of motion. Mass is the measure of inertia.
If you are not moving while you are hanging from the clothesline then the force of tension upwards must euql the force of weight downwards.
A clothesline is under tension when you hang from it. Why is the tension greater when the clothesline is strung horizontally than when it hangs vertically?
mass
A measure of an object's inertia; also a measure of the amount of matter in an object. Depends only on the amount of and kind of particles that compose an object- not on its location (as weight does).
No. The elephant, which has a larger mass, would apply more force to you than the mouse. It has greater inertia and so it will continue to move while the mouse, with smaller inertia, would stop faster with colliding with you.
An elephant and a mouse would both have zero weight in gravity-free space, If they were moving toward you with the same speed, would they bump into you with the same effects?
It has twice the mass, inertia, and weight.
Does a 2-kilogram rock have twice the mass of a 1-kilogram rock? Twice the inertia? Twice the weight?
A liter is a liter so they have the same volume. A liter of lead would have much, much more mass than a liter of apple juice because its density is much greater.
Does a liter of molten lead have the same volume as a liter of apple juice? Does it have the same mass?
Both. Things that are at rest want to stay at rest such as boulders and stubborn mules. Things moving want to keep moving such as a charging elephant or a linebacker in football.
Does the law of inertia pertain to moving objects, objects at rest, or both?
law of inertia
Every body continues in its state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by a net force exerted upon it. Also known as Newton's first law.
normal force
For an object resting on a horizontal surface, the upward force that balances the weight of the object; also called the support force.
support force
Force that completely balances the weight of an object at rest.
15 N - 10 N = 5 N
Forces of 10N and 15N act in opposite directions on an object, what is the net force?
10N + 15 N = 25 N
Forces of 10N and 15N in the same direction act on an object. What is the net force on the object?
Without friction it will get the same height every time
Galileo found that a ball rolling down one incline will pick up enough speed to roll up another. How high will it roll compared with its initial height?
If you split your body weight among both arms, they will each hold up half your weight. If you hold all your weight by one arm, then it will hold all your weight.
How does the tension in your arms compare when you let yourself dangle motionless by both arms and by one arm?
At your feet as well. When the bus is still, the coin is still. When the bus is moving forward, the coin is moving forward at the same speed as the bus the whole time. Everything in the bus is moving forward: driver, passengers, seats, wallets, etc.
If you hold a coin above your head while in a bus that is not moving, the coin will land at your feet when you drop it. Where will it land if the bus is moving in a straight line at constant speed?
None, according toto Newton's First Law, An object will continue moving unless acted on by an external force. There is no friction in space.
If you were in a spaceship and launched a cannonball into frictionless space, how much force would have to be exerted on the ball to keep it going?
newton
SI unit of force. One newton (N) is the force applied to a one-kilogram mass that will produce an acceleration of one meter-per second per second.
net force
The combination of all the forces that act on an object
weight
The force on a body due to the gravitational attraction of another body (commonly Earth).
friction
The force that acts to resist the relative motion (or attempted motion) of objects or materials that are in contact
There is a force, called friction, which is slowing down the bike. If you want to overcome one force, you must apply another.
The law of inertia states that no force is required to maintain motion. Why, then, do you have to keep pedaling your bicyckle to maintain motion?
It remains constant. There is nothing to accelerate/decelerate it
The speed of a ball increases as it rolls down an incline and decreases as it rolls up an incline. What happens to its speed on a smooth, horizontal surface?
Natural motion is straight up and down, light things went up and heavy things went down. Violent motion is imposed: collisions, pulling, and pushing
What distinction did Aristotle make between natural motion and violent motion?
It slows them down
What is the effect of friction on a moving object?
The forces in opposite direction cancel out and the net/resultant force is zero.
What is the net forceor, equivalently, the resultant force acting on an object in equilibrium?
2 x 9.8 m/s^2= 19.6 N
What is the weight of 2 kilograms of yogurt?
Weight varies depending on the distance you are from the center of the earth. The farther away you are the less you weight. Mass doesn't change because of location.
Why do physicists say mass is more fundamental than weight?
To escape religious persecution which considered the earth as the center of the universe
Why was Copernicus reluctant to publish his ideas?
Equilibrium
a state of balance.
Force
any influence that tends to accelerate an object; a push or pull; measured in newtons. A vector quantity.
Newton's first law
law of inertia
