Download Chapter 7 Study Guide: Forces Focus on the highlighted terms and

Chapter 7 Study Guide: Forces
Focus on the highlighted terms and key concepts.
7.1 The Nature of Force
*Like velocity and acceleration, a force is described by its strength and by the direction in which it acts.
*A nonzero net force causes a change in the object’s motion.
force-a push or a pull
newton-(abbreviated N)-the strength of a force, (the unit for force, named after Sir Isaac Newton)
net force-the combination of all the forces acting on an object
Be able to figure out the net force acting on an object. Ex: 50N and 80 N would equal a net force of 30N 
Ex2: 14N and 6N would equal a net force of 20N . See textbook for more examples.
7.2 Friction and Gravity
*Two factors that affect the force of friction are the types of surfaces involved and how hard the surfaces are
pushed together.
*Two factors affect gravitational attraction between objects: their masses and distance.
A gravitational force exists between any two objects in the universe; you only see the strongest forces acting.
As distance between two objects increases, the force between them decreases. As mass increases, force increases.
friction-the force that one surface exerts on another when the two rub against each other is called
mass-the amount of matter in an object is called its
gravity-the force that pulls objects towards each other; pulls falling objects toward Earth
weight-the force of gravity on a person or object on the surface of a planet is called
Types of Friction
sliding friction-occurs when two solid surfaces slide over each other. Ex:The friction between the sled and the snow
as a child sleds down a hill.
rolling friction-occurs when an object rolls across a surface. Ex:The friction between your bike tires and the road as
you ride.
fluid friction-occurs when a solid object moves through a fluid or through the air. Ex:The friction between water and
a swimmer diving into a pool.
static friction-occurs between objects that aren’t moving. Ex:The friction between a box and the ground as you try
to move it, but it does not move.
Be able to recognize or give examples of the types of friction.
Lesson 7.3: Newton’s Laws of Motion
*Newton’s First Law of Motion: Objects at rest will remain at rest and objects moving at a constant velocity
will continue moving at a constant velocity unless they are acted upon by nonzero net forces. It is also called
the law of inertia.
inertia-the resistance to changes in motion Ex: what you feel when the car you are riding in suddenly slows or stops.
*Newton’s Second Law of Motion: The acceleration of an object depends on its mass and on the net force
acting on it.
Acceleration= net force ÷ mass ; Net force= mass x acceleration; mass= net force ÷ acceleration
*Newton’s 3rd Law of Motion:If one object exerts a force on another object, then the second object exerts a
force of equal strength in the opposite direction on the first object. It is also stated as: “for every action there
is an equal and opposite reaction.”
Be able to calculate acceleration, net force, or mass, using the formulas given and two other parts.
Ex: What is the net force on a 4kg bicycle accelerating at a rate of 2m/s2? Ans:(f=m x a) 4kg/2m/s2=2N
Ex: If a net force of 200N acts on a 50kg vehicle, what will the acceleration of the vehicle be?
Ans: a = f ÷ m 200N ÷ 50kg = 4m/s2