Download Forces and Motion Exam – Study Guide

Forces and Motion Exam – Study Guide
The Driving Questions from this unit
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How can motion be described?
How many different kinds of motions are there and what distinguishes them
from one another?
If we roll a car down a hill, will it move at constant velocity or will it
accelerate? Why do you think so?
Does the steepness of the hill make a difference in how the car will move?
Why do you think so?
How could we find out if your ideas are correct?
What is force?
What is the nature of force (i.e. where do forces come from)?
What is the natural state of objects in regard to their motion?
Under what conditions will an object move with constant velocity?
Under what conditions will an object accelerate?
How do the forces that objects exert on one another compare?
How is acceleration related to force and mass?
What determines the rate at which objects fall?
What kind of motion do falling objects exhibit?
What determines the strength of the gravitational forces on objects?
What is air resistance and what factors influence it?
What effect does air resistance have on falling objects?
Define/explain the following terms:
Motion
Reference Point
Position
Distance
Displacement
Speed
Velocity
Acceleration
Force
Unbalanced Force
Inertia
Mass
Frition
Centripetal Force
Air Resistance
Terminal Velocity
Compound Machine
Be able to
 Explain what is described by each of Newton’s 3 Laws of Motion
 Analyze the motion represented on position vs. time graphs
 Analyze the forces acting on an object and predict the kind of motion that
will result.
 Identify the six simple machines and give “real life” examples of each
 Describe how Mechanical Advantage applies to simple machines
 Describe how Mechanical Efficiency applies to machines
Here are some common MISCONCEPTIONS related to force, do you still hold any
of them?
 The only "natural" motion is for an object to be at rest. WRONG!
 If an object is at rest, no forces are acting on the object. WRONG!
 Only animate objects can exert a force. Thus, if an object is at rest on a
table, no forces are acting upon it. WRONG!
 Force is a property of an object. An object has force and when it runs out of
force it stops moving. WRONG!
 The motion of an object is always in the direction of the net force applied to
the object. WRONG!
 Large objects exert a greater force than small objects. WRONG!
 A force is needed to keep an object moving with a constant speed. WRONG!
 Friction always hinders motion. Thus, you always want to eliminate friction.
WRONG!
 Rocket propulsion is due to exhaust gases pushing on something behind the
rocket. WRONG!
 Acceleration always means that an object is speeding up. WRONG!
 Acceleration is always in a straight line. WRONG!
 Acceleration always occurs in the same direction as an object is moving.
WRONG!
 If an object has a speed of zero (even instantaneously), it has no
acceleration. WRONG!
Here are some things to know about Simple Machines.
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What is the difference between class 1, class 2, and class 3 levers? 
A CLASS-1 LEVER has the fulcrum located somewhere between the effort
and the load. With this kind of lever, the direction of force is changes.
Effort applied downward moves the load up. Effort applied upward moves
the load down.
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A CLASS-2 LEVER has its fulcrum at one end of a lever arm. The load is
between the fulcrum and the effort. With this kind of lever, the direction
of effort is not changed. Pushing up on the class-2 lever arm pushes up on
the load. Pushing down on the lever arm pushes down on the load. To gain a
mechanical advantage, the load is places closer to the fulcrum than to the
effort. The class-2 lever always reduces effort.
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In a CLASS-3 LEVER, the fulcrum is at one end, and the effort is applied
between the fulcrum and the load. With this kind of lever, the direction of
effort is not changed. The load moves in the same direction as the effort.
The gain offered by a class-3 lever is one of distance.
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Explain why a simple machine makes work easier to do but does not save
energy.
Most simple machines do not save energy. They distribute the force
needed to do work over a longer distance. Generally, simple machines
can help us in two ways. We can apply less effort over a greater
distance, or we can apply more effort over a shorter distance. Simple
machines provide a gain in effort or a gain in distance. In addition, some
simple machines change the direction of effort.
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How does a lever or pulley give you mechanical advantage?
Sometimes we may want to lift, push, or pull an objects, or we may
need to break or cut them. Some of these jobs require a lot of force.
When we use simple machines, we gain a mechanical advantage by
increasing the amount of force we can bring to bear on an object.
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Mechanical efficiency measures the effectiveness of a machine in
transforming the energy and power that is input to the device into an output
force and movement. Efficiency is measured as a ratio of the measured
performance to the performance of an ideal machine:
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The ideal machine has an efficiency of 100%, because there is no power loss.
Real devices will have efficiencies less than 100% because rigid and
frictionless systems do not exist. The power losses in a transmission or
mechanism are eventually dissipated as heat.