FORCES Lesson 1 Friction and Gravity
Dec 22, 2015
CONTACT FORCES (P.44)
Does not require contact:
NON-CONTACT FORCES (P.46)
Force through CONTACT:
*Virtually all actions require a…
Magnetic:Static
:
Gravity:
Forces are measured inNEWTONS
GRAVITY (P.47)
An attractive force that exists between all objects that have mass.
This force is dependent on mass and distance from the object.
WEIGHT VS MASS (P. 48)
What is the difference?
Weight: Is the gravitational force exerted on an object.
Your weight is actually a force measured in Newton’s.
Mass:
Amount of matter in an object.
Demonstration: Mass & Gravity
LINK
GRAVITY AND AIR RESISTANCE
Most objects falling through air experience a type of fluid friction called air resistance.
Air resistance is not the same for all objects. The greater the surface area of the object the
greater the air resistance. (paper drop)
However, since the elephant has more mass, it has more downward force of gravity and falls faster.
GRAVITY AND FREE FALL
An object is in free fall when the only force acting on the object is gravity.
Free-falling objects do not encounter air resistance.
In free fall, the force of gravity is an unbalanced force.
Gravity Tube Demonstration
Take away ALL air, so that only the force ofGravity is beingused.
TRY THIS
CALCULATING FREE FALL
All objects in free fall accelerate at the same rate – 9.8 m/s² - regardless of their mass.
in one second = 9.8 m/s²
in two seconds = 19.6 m/s²
in three seconds = 29.4 m/s²
in four seconds = ________
The velocity continues to increase as the object falls.
UNIVERSAL GRAVITATIONThe law of universal gravitation states that the force of gravity acts between all objects in the universe.
(1:47 min)
WHAT IS FRICTION? (P.49)
Friction is a force that resists the motion of two surfaces that are touching.
When a moving object comes in contact with another object, friction is the opposing force that slows or stops the moving object.
*Static..prevents objects sliding
*Sliding...resists objects while they are moving
*Fluid…air or water
Without friction, an object would continue to move at constant speed forever.
The strength of the force of friction depends on the type of surfaces and how hard the surfaces push together.
Rough surfaces produce greater friction than smooth surfaces.
TRY THIS
WAYS TO REDUCE FRICTION
Smooth the surface / Put ball bearings in wheels
Replace rolling with sliding / Add oil or another type of lubricant
(5:41 min)
FrictionInDailyLife