Forces Slide 2 Change in motion? What causes an object to start
moving, stop moving, or change direction? UNBANLANCED FORCE Slide 3
What is a force? A push or pull A force is described by strength
and direction The strength of a force is measured in the Newton (N)
Arrows are used to represent force: Slide 4 Combining forces Most
of the time, there are more than 1 force acting on an object at a
time Net force- the combination of all forces acting on an 15 N
Slide 5 Unbalanced vs. Balanced Forces Unbalanced Forces Result in
a net force Can cause a change in the objects motion Balanced
Forces Equal forces acting in opposite direction Do not cause a
change in the objects motion They cancel each other out Slide 6
Draw Force Diagrams in Notebook 1. A book is at rest on a tabletop.
Diagram the forces acting on the book 2. A gymnast is holding on
the rings suspended from the ceiling waiting to being. 3. A flying
squirrel is gliding (no wing flaps) from a tree to the ground at
constant velocity. Consider air resistance. 4. A rightward force is
applied to a book in order to move it across a desk at constant
velocity. Consider frictional forces. Neglect air resistance Slide
7 Examples Continued 5. A student rests a backpack upon his
shoulder. The pack is suspended motionless by one strap from one
shoulder. 6. A skydiver is descending with a constant velocity.
Consider air resistance 7. A force is applied to the right to drag
a sled across loosely packed snow with a rightward acceleration 8.
A car is coasting to the right and slowing down Slide 8 Formula
F=ma Force = mass x acceleration Units: Newtons (N) N=(kg)(m/s 2 )
Slide 9 Friction Force that oppose motion- always in opposite
direction of motion The force that one surface exerts on another
when the two surfaces rub against each other Slide 10 Friction
Friction produces heat! how have you seen this? The amount of
friction depends on: How hard the surfaces push together (force)
Types of surfaces involved SURFACE AREA DOES NOT AFFECT THE AMOUNT
OF FRICTION Slide 11 Static Friction Acts on an object that are not
moving Strongest- most difficult to overcome Examples: Desk on the
floor Parked car on the pavement Slide 12 Sliding Friction Occurs
when one solid surface slides over another solid surface Not as
strong as static friction Examples: Bicycle brakes Pushing a box
along the floor Slide 13 Rolling Friction Occurs when an object
rolls over a surface Not as strong as sliding friction Examples:
Shopping cart Car traveling on the road Slide 14 Fluid Friction
Occurs as an object moves through a fluid Examples: Surf boarding
in the ocean Car as it moves through the air Slide 15 Gravity Is
the force that pulls objects toward each other The law of Universal
Gravitation- the force of gravity acts between all objects in the
universe! That means: any two masses exert an attractive force on
each other Slide 16 Factors affecting gravity Mass- a measure of
the amount of matter in an object The more mass an object has, the
greater its gravitational force on other objects is Distance The
farther apart objects are, the lesser the gravitational force
between them The sun has a gravitational force on you..why dont you
feel it? The pencil in front of you has a gravitational force on
youwhy dont you feel it? Slide 17 Gravitational Acceleration The
gravitational attraction of Earth causes all falling objects to
have an acceleration of 9.8 m/s2 Which direction is Earths
gravitational force? Slide 18 Weight What is it? The gravitational
force exerted on an object W=m x g g=a Calculate the weight of a
truck with a mass of 600 kg. G: m = 600 kgF: W=m x g g = 9.8 m/s/s
Find: w = ?W.S.: w = 600kg x 9.8 m/s/s Answer: 5,880 N Slide 19
Mass vs. Weight Mass is _________ Weight is a FORCE the more mass
an object has, the stronger the gravitational force between the
object and Earth. So, the more mass an object has, the more it
weighs Weight can be different if the gravitational force is
different Slide 20 Weightlessness When an object is influences only
by the force of gravity, it is said to be in free fall. Slide 21
Air resistance Air resistance acts in the opposite direct of an
objects motion The force it opposes is GRAVITY The amount of air
resistance depends on: Speed Size Shape Terminal velocity- when the
force of air resistance = weight of object no more acceleration
Slide 22 What happens if you drop 2 objects? What would happen if
there was no air resistance? REMEMBER: ALL OBJECTS IN FREE FALL
ACCELERATE AT THE SAME RATE, REGARDLESS OF MASS!! Slide 23
Projectile Motion A projectile is an object that has been projected
through the air A projectile has horizontal and vertical motion
Neglecting air resistance, all falling objects accelerate at the
same rate No matter how fast and object is moving horizontally, the
force of gravity acts the same as if it was falling straight
down
