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Name:_________________
Date:_________________
Physics 11 - Unit 4 FORCES
4.1 – Newton’s Laws of Motion
A force is a __________________ or a ____________________.
Vector
or
Scalar
?
Symbol:____________
Units: ___________
What causes acceleration?
_________________________________________________
Definition of
_________________________________________________________________________________
_________________________________________________________________________________
________________________________________________________________________
No matter what causes the force it is always measured in units of Newtons (N) after Sir Isaac
Newton a brilliant physicist of the 1600's. The units of force are a compound unit that means the
Newton is made of basic units such as kilograms, meters and seconds. In fact a Newton is defined
as a kilogram meter per second per second or: 1N = 1 kg.m / s2
What are some common forces?
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The most common force which we encounter every day is the _________________________________
A second force we encounter but often do not consider outside of the physics class is the
__________________________________ This is the force which a surface exerts to hold up an object.
On a HORIZONTAL surface___________________, this is because the object moves neither up
nor down from the surface so these two forces must be in balance.
A third common force is the___________________. This force always _____________
and acts to decelerate objects. _____________where is called the coefficient of friction,
this simply describes how much two surfaces stick together. has no units. Fn is the
normal force of one surface supporting the other measured in newtons.
Another force for physics 11 students is the________________, which tries to snap objects
to their original shape when you stretch or compress them._______________, here k is
called the spring constant which describes how easily an object may be stretched or
compressed measured in newtons per meter (N/m). And x is the distance the object is
stretched or compressed measured in meters.
The equations for the various forces are summarized in the table below.
Force Name
Symbol Formula
Force of Gravity
Fg
Fg = mg
Normal Force
Fn
Fn = Fg on a horizontal surface
Force of Friction
Ff
Ff = Fn
Elastic Force
Fe
Fe = kx
______________________ - an object with no net force acting on it remains at rest or moves with
constant velocity in a straight line. (No acceleration)
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
___________________________________________________________________
_______________________________ - the acceleration of a body is directly proportional to the
net force on it and inversely proportional to its mass.
___________________________________________________________________________
Equation: _______________________
Ex. 1) Find the net force in the following diagrams:
____________
____________
Ex 2: What net force is required to accelerate a 1500 kg race car at 3.00 m/s ?
Ex 3: An artillery shell has a mass of 55 kg. The shell is fired from a gun, leaving the barrel with a
velocity of 770 m/s. The gun barrel is 1.5 m long. What is the force on the shell while it is in the
gun barrel?
1. Read pgs 87 – 91
Do pg 92 #1 – 4