PHYSICS: NEWTON’S LAWS Flashcards
Newton’s first law
The law of inertia
-classical mechanics is based on the application of newtons laws
-the law of inertia states that objects in motion tend to stay in motion and that objects at rest tend to stay at rest
-inertia is the property of matter that resists any change in motion
Newton’s second law
-describes the relationship between force, mass, and acceleration
-states that the force applied on an object = the mass of the object times its acceleration
- force = mass X acceleration or f=ma
-explains why a small car has better gas mileage than a big car
-according to this law, the force required to accelerate the big car (with the greater mass) is greater than the force required to accelerate the small car
-the big car therefore has to burn more gas and it’s engine to produce the additional force
Newton (N)
-unit that represents a force that accelerates a mass of 1 kg, 1 m/s
Friction
-whenever force is exerted on an object along a surface or whenever an object has a velocity along the surface, and the two surfaces touch, there is a force called friction
-in the case of the box being pushed along the floor, friction opposes the motion of the force being applied
-note that the force of friction is always in the direction to stop the object from moving
Gravity
-force of attraction between all objects in the universe
-the greater the mass of an object is, the greater its gravitational force will be
-the earths gravitational force is great because the earth has a large mass
-if you drop an object, it falls to the earth because the earth exerts the gravitational force on it
-the force due to gravity is not the same on every object but depends on the objects mass
-however, the acceleration toward earth is the same for all objects independent of their mass
Weight
-the pull of gravity on an object determines its weight
-a change in the force of gravity results in a change in an objects weight but not in its mass
-ex. the earth has more mass than the moon so the earth exerts a greater gravitational force than the moon
-on the moon you would weigh about 1/7 of what you would weigh on earth because the gravitational pull of the moon is about 1/7 of the gravitational pull of the earth, yet your body mass would stay exactly the same as it is on earth
-the force of gravity between two objects decreases as the distance between the object increases
-ex. the earths gravitational pull on a rocket decreases as the rocket moves away from the earth
-a way to compare substances in terms of heaviness so that they are comparable is to use density, which is:
mass per unit volume: density = mass / volume
-a pound of iron and a pound of feathers both way a pound however a pound of feathers may take up much more space than the iron
Torque
-the ability of a force that is applied perpendicularly to rotate an object around an axis, such as using a wrench to turn a bolt, is measured by a quantity called torque
-torque is the perpendicular force times the lever arm
-the lever arm is the distance from the axis of rotation to the point where the force is exerted (e.g., the length of the wrench)
-the farther the forces from the axis of rotation, the easier it is to rotate the object and the more torque is produced
The centripetal force
-to keep a ball at the end of a string moving in a circle, you must continually exert a force pulling the ball back toward the center of the circle
-force is called the centripetal force and in the case of the ball on a string, the string provides the force
Newton’s third law of motion
-states that for every action there’s an equal and opposite reaction
-a rocket works on this principle, the blast from the back of the rocket pushes the rocket forward
Energy
In mechanics, objects are defined as having energy
-energy is the ability to do work
Kinetic energy
-energy associated with motion
-any moving body has this type of energy because it is able to do work by moving other bodies
-the kinetic energy of a body tells us how much work that body can do by moving other bodies until it is brought to rest
-kinetic energy is defined as one half of the product of mass and the velocity squared:
- Kinetic energy = 0.5 x mv^2
Mv (mass velocity)
Potential energy
-energy stored in a body because of its position
-when you lift an object up, you provided with potential energy
-an object has more potential energy at the top of the building than it does on the floor
Work
-when you do work on an object, you change its energy by giving it some of your energy
-work is defined as the product of the force applied to an object and the distance through which the force is applied
- work = force X distance
Joule
The unit of energy equal to the work done by a force of 1 newton acting over distance of 1 meter
Power
-rate at which work is done
-the power of a machine is the total work done divided by the time taken
-since work equals force times distance the formula for power is:
power = force X distance / by time = work / time
