Download 15.2 Forces study guide KEY

Name_______________________________ period _________ date _____________
Study guide for Chapter 2 Test: Forces
Force
A push or pull, some are contact forces (pushing a cart) and others are non-contact forces
(electric force, magnetic force, gravity)
Newton
The unit used to measure force. Named after Isaac Newton.
Net Force
The combination of all the forces acting on an object, the TOTAL force on an object.
Balanced Forces (what they are and what effect they have on an object’s motion)
When all the forces on an object cancel each other out.
Balanced forces do NOT cause a change in motion.
If an object was still- it stays still with balanced forces.
If the object was moving and the forcces become balanced, the object keeps
moving at a constant speed and direction.
Unbalanced Forces (what they are and what effect they have on an object’s motion)
When the forces on an object are unequal.
Unbalanced forces DO cause a change in motion. Unbalanced forces cause an object to
accelerate (speed up, slow down, or change direction)
Terminal velocity (what it is and what has to happen to the forces on an object)
The top speed an object reaches when being pulled downward by gravity. It occurs when
gravity and air resistance (fluid friction) equal each other. When terminal velocity is
reached, acceleration is at zero.
Inertia
The tendency (habit) of matter to resista a change of motion. It takes an unbalanced force
to cause an object to change its motion and overcome inertia.
Friction (what it is, why it happens, and how to increase or reduce friction)
The force that opposes motion, that resists or opposes motion.
It occurs because surfaces are never completely smooth and the surfaces “catch” on each
other.
Name_______________________________ period _________ date _____________
• One thing that affects friction is the force between the surfaces and as it increases,
friction increases.
•
Another factor that influences friction is the surface area between the surfaces,
and as it increases friction increases.
•
The third factor that influences friction is roughness or stickiness, and as it
increases, friction increases.
Four types of friction and examples:
In general,
the amount
of friction
decreases
as you
move down
this list of
4 types.
o Static: When an object is resisting motion, and not yet moving.
§
Ex. Pushing a heavy piece of furniture.
o Sliding: When 2 solids slide past each other.
§
Ex. Sliding down a slide at the playground, erasing pencil marks.
o Rolling: When one of the objects is round.
§
Ex. Wheels of any type, rollers in a factory, ball bearings
o Fluid: (Make sure you know that both ___liquids__ and __gases__ are
fluids.) When one of the substances is a fluid.
§
Ex. Swimming, air resistance when biking
The two factors that affect gravity and how they affect gravity.
•
One thing that affects gravity is ___distance___ and as it increases,
gravity ___decreases______
•
The other factor that influences gravity is ___mass______ and as it
increases, gravity ___increases____.
Newton’s 3 Laws of Motion (Know and be able to apply all three laws.)
1st law: An object in motion will stay in motion and an object at rest will stay at
rest until acted upon by an unbalanced force. It takes an unbalanced force to overcome
inertia and make an object accelerate (speed up, slow down, change direction)
2nd law: The acceleration of an object depends on the force applied to the object
and the mass of the object.
Name_______________________________ period _________ date _____________
• If the mass of an object increased, but the force on it stayed
constant then the acceleration of the object would ___decrease___.
o Ex: Car vs. Truck race but both have the same engine. Car
will have more acceleration and win.
•
If the force on an object increased, but the mass of the object
stayed the same then the acceleration would ___increase___.
o Ex. Push my sister on the swings soft vs. hard. Stronger
push will accelerate her more.
•
If the mass doubled and the force was cut in half, then the
acceleration would ____be reduced to 1/4_______.
o Push a cart filled with 2x the groceries, but have my son
(smaller, weaker) push it with ½ my force and the cart will
accelerate only ¼ as much.
3rd law: For every action there is an equal and opposite reaction.
***Action/Reaction forces do NOT act on the same object. They are not balanced forces,
because they act on separate objects.***
•
If an action force was __the wind___ pushing/pulling on ___a windmill____.
•
The reaction force would be ___the windmill______ pushing/pulling on ____the
wind (air molecules)____.
•
The result of the action force would be: the windmill starts to turn.
•
The result of the reaction force would be: the air molecules slow down
when they hit the windmill.