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Click on the document below to see Essential vocabulary for unit 1


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Identifying Forces

Solving Problems involving Constant Velocity

Solving Problems involving Constant Acceleration


Desert

Block pulled at a constant speed problems

Incline Plane Problems

Elevator Problems

UnderConstruction

Pulled Block ProblemChoose from the following options

Block Pulled at a constant velocity with NO vectors

Block Pulled at a constant acceleration with vectors

Block Pulled at a constant velocity with vectors

Block Pulled at a constant acceleration with NO

vectors

60 Degrees

Pulled Block Problem

Problem Solution

Block Pulled at a Constant VelocityVectors

A block with a mass of 150kg is pulled to the right with a force of 200N at an angle of 60 degrees above the horizontal. If the block has a constant velocity of 9 meters per second, determine the weight of the block, the normal force acting on the block , and the force of friction acting on the block

150 kg-100 N

1297 N

1470 N

200 N

1. To begin click the ‘problem’ button

2. When finished, hit ‘solution’ to see the answer

3. Hit ‘problem’ again to get a new problem

4. Hit the Back button to go back to the type of problem menu

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Elevator Problem

Problem

Solution

A 60kg person is riding in the elevator depicted below. What is the apparent weight of the rider while the elevator is accelerating downwards with a constant acceleration of 3 meters per second squared?


2. Hit ‘Free-Body Diagram’ to view the Free-Body diagram for this problem

3. Select Fnet equation to view the equation used to solve the problem



6. Hit the coffee cup to return to the previous menu

Free-Body Diagram

Fnet Equation

Apparent Weight=

Incline Ramp Problem

Problem

Solution

A 430kg block is at rest on a ramp with an incline of 30 degrees. Determine the acceleration of the block if the coefficient of static friction is 1.22 and the coefficient of kinetic friction is 0.58.


2. Hit ‘Free-Body Diagram’ to view the Free-Body diagram for this problem

3. Select Fnet equation to view the equation used to solve the problem



6. Hit the coffee cup to return to the previous menu

Free-Body Diagram

430kg

F┴

Fg

Fnet Equation

0 gyFFAcceleration= 0

meters per second squaredmaFF gxF

FF

Vertical Fnet

Horizontal Fnet

30 Degrees

Fgy

Fgx

Identifying Forces“The sources of Forces”

Identifying ForcesObjective:

To recognize what are the sources of forcesTo be able to for any given object and situation,

correctly identify what forces are acting.

Identifying Forces There are three sources to consider when

thinking about what forces are acting on an object.

1. First consider any gravitational forces2. Second ask yourself what is in contact with

the object3. Finally, are there any frictional forces to

consider

Identifying Forces(Gravity)Gravity

Gravitational Forces exist if the object is located in a gravitational field.

For our purposes at this point, all objects on the earth are subject to gravity.

One note about gravity, it behaves differently then all of the other forces we are studying. It can act without contact

The symbol for the force of gravity is Fg

Identifying Forces(Gravity)

If gravity is present it always pulls an object straight down. It never acts at an angle.

Fg

Fg

Fg

Fg

Fg

Identifying Forces(Gravity) The force of gravity is called the weight of an object. When using the word weight in physics, you are referring to the downward pull on

that object caused by the force of gravity. Weight and mass are NOT the same thing!!!!!!!

The reason this is confusing is because mass and weight are related concepts. The more mass something has the more it weighs. It is important to understand the difference in terminology and what is meant by each word. Remember physics vocabulary is specific and we have specific words for different things to eliminate vagueness.

Weight Mass

The downward pull of gravity on the object

The amount of matter an object possess

The value of the weight fluctuates as the strength of the gravitational pull changes

The value of an objects mass doesn’t change based on gravitational changes.

Identifying Forces (Contact)Contact Forces are caused by anything in

contact with the object.They are a result of Newton’s third law.They always act in the direction opposite the

location of the object.As a result of Newton’s Third law, all

exchanged contact forces between two objects are equal and opposite.

The symbol for a contact for is always F with a subscript letter representing what is in contact

Identifying Forces (Contact)The symbol for a contact for is always F with a subscript

letter representing what is in contact. The subscript is up to you but it should make sense. Sometimes a subscript of a few letters or even a whole word is used for clarification.

The table below includes a few example contact forces and the symbol that is frequently used.

Contact Force Symbol

Air Resistance Fa

Table Ft

Rope Fr

Ground Fgr

Identifying Forces (Contact)

When identifying contact forces, ask yourself how many objects are in contact. For every object in contact , add one contact force

Fground

FgroundFAi

r

FAi

r

FAi

r

FAi

rFAi

r

FAi

rFAi

r

Froa

d

Frop

e Frop

e

Frop

e


Observe the use of Newton’s 3rd Law with the pictures of the car driving and the jets flying. In both cases the forward motion is a result of contact between them and something else.

Fground

FgroundFAi

r

FAi

r

FAi

r

FAi

rFAi

r

FAi

rFAi

r

Froa

d

Frop

e Frop

e

Frop

e


Observe the use of Newton’s 3rd Law with the pictures of the car driving and the jets flying. In both cases the forward motion is a result of contact between them and something else.

FgroundFAi

r

FAi

r

FAi

r

FAi

rFAi

r

FAi

r

Froa

d


For the car, the forward force is caused by the car’s tires gripping the road and pushing the road backwards. As a result of Newton’s 3rd law, the road pushes the car forward with equal force. It is the road that pushes the car forward.

Fground

FAi

r

FAi

r

FAi

r

FAi

rFAi

r

FAi

rFAi

r

Froa

d


For the jet, the forward force is caused by the air the jet engines are pushing backwards as exhaust. As a result of Newton’s 3rd law, the air pushes the jets forward with equal force. This is similar to the car.

Fground

FAi

r

FAi

r

FAi

r

FAi

rFAi

r

FAi

rFAi

r

Froa

d

Identifying Forces (Contact)The Normal Force

In physics, the contact interaction with a surface is an import concept. Several additional concepts are linked to this interaction.

Because of this importance, this contact force is given a special name. The Normal Force.

The symbol for the Normal Force is F┴

Normal Force can be identified either with a subscript identifying the object or with the perpendicular subscript.


FAi

r

Froa

dSo either label it this way

Ftable

Fground

Fground


F┴

FAi

r

Froa

d

Or label it this way

F┴

F┴

Identifying Forces (Friction)Frictional Forces exist if the following two

conditions are true1. The object is in contact with a surface.2. The object is either moving or attempting to

move. Frictional Forces always act against motion. Frictional Forces are designated FF

Identifying Forces (Friction)

There is a frictional force present here

because Jimmy Rollins is both in

contact with a surface(the ground)

and is moving.FF


Once he stops moving, the

frictional force will disappear until he attempts to move

againFF


There is no frictional force acting on these blocking sleds.

Although they are in contact with the ground, they are

stationary and not attempting to

move.

Identifying Forces (Friction)Once the football

players start pushing the sled, there is a frictional force.

Although the sled depicted here is stationary, it is

attempting to move. You determine if an

object is attempting to move by asking

yourself, if I eliminate friction, would the

object accelerate. If so, then it is

attempting to move.

FF


In the is case, since the football players are pushing the sled

left, without friction it would accelerate left.

Therefore there is friction

FF

Identifying Forces (Summary)There are three sources of forces

1. Gravity2. Contact3. Friction

When constructing a Free-body diagram consider each category and think about if any of these forces are present.

Identifying Forces (Summary)

Click here for answer?

What forces are acting on the

chemistry book?

Identifying Forces (Summary)

Click here for answer?

What forces are acting on the

chemistry book?

Fg

FCalculas

FPsychology Book

Identifying Forces

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As the football players push

harder the sled will begin to slide. The force of friction has a max value. It will

increase in strength up to that

point.

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