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# Chapter 12 Forces

### Forces

Any push or pull on an object Force
The net force exerted on an object will produce a proportional acceleration. That is, if a force acts on something, it accelerates. Newton’s 2nd Law of Motion.
What explains the relationships among mass, force and acceleration? Newton’s 2nd Law of Motion – F(force) = m (mass) • a (acceleration)
The force that opposes motion between two surfaces in contact with (sometimes rubbing against) each other Friction
Type of friction between 2 surfaces that are NOT moving past each other Static Friction – Static means stationary, not moving
Type of friction between 2 surfaces that are sliding past each other Sliding Friction – example: When a car skids, its locked wheels slide over the road surface.
Type of friction between the wheels of a car in motion and the road Rolling Friction – In this example, the wheels of the car are moving, or rolling.
The force exerted by air on a moving object Fluid Friction - also called air resistance and drag
The largest velocity reached by a falling object when the force of air resistance equals the force of gravity Terminal velocity
The force every object in the universe exerts on every other object Gravity
The pull of gravity on an object is its __________. Weight
The amount of matter in an object is its _______. Mass
Mass is also a measure of the _______, or resistance to change in motion of an object. inertia
The SI unit for mass is g or kg
The SI unit for weight is N - newtons
The Si unit for acceleration is usually m/s2
The SI unit for velocity m/s or km/h
Is force a vector or scalar quantity vector - it needs direction
What law can be stated as “to every action, there is an equal and opposite reaction”? Newton’s 3rd Law of motion
The property of a moving object resulting from its mass and velocity Momentum (p= m • v)
In the formula p= m • v, what does the p stand for? Momentum
What is the SI unit for momentum kgm/s
The Newton, the SI unit for force can also be written as the units for m x a combined. What is that? kgm/s2
What force keeps moons in orbit around the planets, the the planets in orbit around the sun? Gravity
In the absence of air, how would objects dropped from the same height fall? At the same rate
If objects of different masses are dropped from the same height (no air resistance), which will hit the ground first? They will hit at the same time.
If a ball and a feather are dropped through the air at the same time, what causes the feather to fall more slowly? air resistance
What is the size of the force of the acceleration of gravity on earth (g)? 9.8 m/s2 towards the center of the earth
How do we measure Mass in Science? We measure mass in kg, using a balance.
How do we measure Weight in Science? We measure weight in Newtons, using a spring scale.
Which one does not change and cannot be zero, mass or weight? mass
Because you are getting further from the center of the earth, as you climb up a mountain, or ascend in a plane, your weight will _____ decrease
What would cause the momentum of a massive object to be 0 N? If the object was not moving, its velocity would be 0 m/s2. Since p= m • v, any mass with a velocity of 0 m/s2 would have a momentum of 0 N.
Use Newtons third law to explain how a rocket moves. The rocket pushes hot gases backwards and the hot gases push the rocket forward.
Use Newton's third law of motion to explain how a person runs. A person's foot pushes the ground backwards and down, and the ground pushes the foot, and the attached person, forwards and up.
What is a free body diagram? A picture of one object showing all the forces acting on that object as vector arrows.
If two forces are acting in the same direction, how do you find the net force? You add the two
If two forces are acting in opposite directions on the same object, how do you find the net force? You subtract them
What if the forces on an object are acting at right angles to each other, how do you find the net force? You must use pathagorean theorum: a squared + b squared = c squared.
What devise do we use to measure forces spring scale
Define net force The sum of all the forces acting on an object
What are some discoveries of Sir Issac Newton laws of motion, universal gravitation, calculus, lenses and diffraction of light
Who discovered things fall at the same rate with his experiments rolling balls down a ramp and dropping them off the tower of Piza? Galileo
Define inertia An objects resistance to change in motion
Why should you wear your seat belt? Because of inertia, if not you will go flying forward in a head on crash as the car stops.
Problem solving: What is the force required to move a 5,000 kg car with an acceleration of 4 m/s2? F = m x a! 20,000 kgm/s2 or 20,000 N
What is the acceleration of a 4,000 kg car pushed with a force of 12,000 N? F = m x a! Solve for a. 3 m/s2
What is the weight of a 4,000 kg car? Remember W = m x g. 39,200 N or 39,200 kgm/s2
What is the momentum of a 110-kg professional fullback running across the line at 9.2 m/s. p = m x v. p is momentum and v is speed or velocity. 1012 kgm/s
What are the 4 universal forces in nature electromagnetic, strong and weak nuclear, and gravity
Draw a free body diagram for a jet flying in the air It should have thrust pointing forward, gravity down, drag backwards, and lift upwards
Draw a free body diagram for a jet parked on the ground It should have gravity pointing down and the ground pointing up
What is the net force on a box with two people pushing on the same side with 5 N of force each to the east. 10 N east (add them)
What is the net force on a box if one person pushes with 5 N east and the other pushed 10 N west 5 N west (subtract them)
What if one person is rowing a boat with 10 N of force east and the river is pushing the boat with 5 N of force south? Use Pythagorean theorem. 5 squared + 10 squared = c squared. 11.18
Created by: tbrandt