Physics 11 - Unit 4 FORCES s1

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?  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