Motion & Forces
All your life force has been acting upon you whether you notice it or not. Whether it is the force of gravity pulling you towards the earths centre, or maybe simply the force of friction.
So...
What exactly is force you may ask?
Well force is anything that can cause or influence an object to undergo change. This change either affects its movement, direction or deform it. Force is always exerted on one body by another and in one direction.
Every time you move something, use your pencil, or walk, you are using force. You use force to pretty much make your life easier! But sometimes, this isn't always the case...
Drawing Forces:
When drawing forces we must always take into account the following:
So...
What exactly is force you may ask?
Well force is anything that can cause or influence an object to undergo change. This change either affects its movement, direction or deform it. Force is always exerted on one body by another and in one direction.
Every time you move something, use your pencil, or walk, you are using force. You use force to pretty much make your life easier! But sometimes, this isn't always the case...
Drawing Forces:
When drawing forces we must always take into account the following:
- The horizontal or vertical line of action is a dotted line.
- The direction of the force is displayed using an arrowhead.
- The magnitude of the force is represented by an arrow or by a number.
- The point in which you apply the force is the starting of the arrow.
This is Bob. Bob is rolling his suitcase full of Hawaiian t-shirts towards the airport. Ready to embark on his tropical vacation, Bob must first move his suitcase towards the ticket counter. In order to create a movement, Bob must apply a force. The force he applies is demonstrated through the red arrow. The point of the arrow head ( his hand) shows us the point in which he is applying the force. 20 N (written above the suitcase) tells us that he is applying 20 N of force towards the handle. And finally, the line of action displayed though the dotted line demonstrates how the suitcase will be moving (in this case it will be moving horizontally and forward).
If you haven't noticed.. Force is measure in Newtons (N).
1N=1KgX1m/s²
Now there are 3 main different types of forces:
1) Gravitational Force: The gravitational force on earth pulls everything towards the centre of the planet. This gravitational pull becomes weaker as the distance from the centre of the earth increases.
Weight: this is a measurement of the gravitational force acting upon an object.
*Note- the gravitational force on earth is 9.8 N\Kg
Mass: is the quantity of matter in a object.
And so.. To calculate weight, you must multiply mass (in Kg!) by the gravitational force of the planet.
If you haven't noticed.. Force is measure in Newtons (N).
1N=1KgX1m/s²
Now there are 3 main different types of forces:
- Gravitational Force
- Electromagnetic Force
- Strong and Weak Nuclear Force
1) Gravitational Force: The gravitational force on earth pulls everything towards the centre of the planet. This gravitational pull becomes weaker as the distance from the centre of the earth increases.
Weight: this is a measurement of the gravitational force acting upon an object.
*Note- the gravitational force on earth is 9.8 N\Kg
Mass: is the quantity of matter in a object.
And so.. To calculate weight, you must multiply mass (in Kg!) by the gravitational force of the planet.
Weight (N) = mass (Kg) X gravitational force (N\Kg)
Examples:
What is the mass of Bob's 10Kg suitcase on earth?
- 10 Kg
What is the weight of Bob's 10 Kg suitcase on earth?
- 10Kg X 9.8 N/Kg = 98 N
2) Electromagnetic Force: the force of attraction or repulsion between 2 objects with an electrical charge or with magnetic poles. This force is responsible for contact forces. A contact force is the result of acting directly on an object.
What is the mass of Bob's 10Kg suitcase on earth?
- 10 Kg
What is the weight of Bob's 10 Kg suitcase on earth?
- 10Kg X 9.8 N/Kg = 98 N
2) Electromagnetic Force: the force of attraction or repulsion between 2 objects with an electrical charge or with magnetic poles. This force is responsible for contact forces. A contact force is the result of acting directly on an object.
When Bob places his laptop on the table, the lap top undergoes many forces such as the electromagnetic force (contact force).
Electromagnetic Force - Friction: Friction occurs between 2 objects whose surfaces are not perfectly smooth, when they come into contact. It it basically the opposite phenomenon of one object slipping over the other.
To set an object into motion, we must overcome friction.
Friction is influence by 2 main factors:
3) Nuclear force: this force holds the protons and neutrons together.
Electromagnetic Force - Friction: Friction occurs between 2 objects whose surfaces are not perfectly smooth, when they come into contact. It it basically the opposite phenomenon of one object slipping over the other.
To set an object into motion, we must overcome friction.
Friction is influence by 2 main factors:
- The nature of the surfaces in contact (the rougher the surface, the greater the friction).
- The intensity of the pressure of each surface on the other (perpendicular force).
3) Nuclear force: this force holds the protons and neutrons together.
Speed, Distance & Time:
When a person covers a distance in a given time, then that person is said to be in motion. The rate in which he/she moves is called speed!
Now the relationship between speed, distance & time can be expressed in two different ways:
We use this method when the speed is not constant over the entire trajectory (distance it covers).
When a person covers a distance in a given time, then that person is said to be in motion. The rate in which he/she moves is called speed!
Now the relationship between speed, distance & time can be expressed in two different ways:
- The first way would be using the average speed:
We use this method when the speed is not constant over the entire trajectory (distance it covers).
V ave = d/Δt
Where...
V ave= average speed (m\s)
d= total distance (m)
Δt= time interval (s)
Where...
V ave= average speed (m\s)
d= total distance (m)
Δt= time interval (s)
- The second way would be using constant or instantaneous speed.
V= d/Δt
Where...
V = constant speed (m\s)
d= total distance (m)
Δt= time interval (s)
Where...
V = constant speed (m\s)
d= total distance (m)
Δt= time interval (s)
Here's an example!
- What is the average speed of a car that travels 10 000m in 600s?
Vectors and Scalars (woooh!)
In physics, there are two kinds of quantities: scalar quantities and vector quantities.
- Scaler only has a magnitude (size). I.e 5.0 Km
- Vector has magnitude as well as direction. I.e 5.0 km. [North]
Scalar
|
Vector
|
Representing Vectors:
Vectors are normally displayed using arrows.
The length of the arrow = magnitude
The point of the arrow= direction
Now...
What happens if you have more than one vector?
Well, you can add them!
There are two different ways you can add vectors:
Draw each vector one after the other, but be sure to include the direction (angle) and the magnitude.
*Note, this drawing must always be to scale!*
Vectors are normally displayed using arrows.
The length of the arrow = magnitude
The point of the arrow= direction
Now...
What happens if you have more than one vector?
Well, you can add them!
There are two different ways you can add vectors:
- Graphically (drawing) : use the head-to-tail method!
Draw each vector one after the other, but be sure to include the direction (angle) and the magnitude.
*Note, this drawing must always be to scale!*
- Adding by components:
To add vectors using components you must follow six steps.
1) Split the vectors into X and Y components.
Step 2: add the X components together (giving the x component of the resultant).
Step 3: add the Y components together (giving the y component of the resultant).
Step 4: Sketch the x and y for the resultant.
Step 5: Calculate the magnitude (using Pythagoras).
Step 6: Find the direction/angle (using tan).
Step 3: add the Y components together (giving the y component of the resultant).
Step 4: Sketch the x and y for the resultant.
Step 5: Calculate the magnitude (using Pythagoras).
Step 6: Find the direction/angle (using tan).
Graphing Motion (Yayyy)
Now before we start graphing motion, I think it would be best if we first went over a few definitions.
Position (d): Where an object is (this is also a vector, meaning is has both direction and magnitude).
Displacement (Δd): change in position, from starting point to finish point (vector).
Δd= df-di
Distance: length of path traveled (this is scaler).
Now in order to complete the majority of the questions associated with graphing motion, you must learn the following equations:
Position (d): Where an object is (this is also a vector, meaning is has both direction and magnitude).
Displacement (Δd): change in position, from starting point to finish point (vector).
Δd= df-di
Distance: length of path traveled (this is scaler).
Now in order to complete the majority of the questions associated with graphing motion, you must learn the following equations:
Time interval = Δ t
Average speed = total distance/ Δ t
Average velocity = Δ d/ Δ t
Acceleration = Δ v/Δ t
Average speed = total distance/ Δ t
Average velocity = Δ d/ Δ t
Acceleration = Δ v/Δ t
Now, there are 3 different types of graphs used the diplay motion:
1) Position vs Time:
- Position vs Time (d-t)
- Velocity vs Time (v-t)
- Acceleration vs Time (a-t)
1) Position vs Time:
- To find the displacement: final position- Initial position
- To find the distance: add up the length of the path.
To find the instantaneous velocity:
- Find the rate of change of the line the point is on.
- Find the rate of change of the tangent line.
2) Velocity vs Time (v-t):
- To find the velocty: read the graph.
- To find the acceleration at one point find the slope.
- To find the displacement or distance: find the area between the line and the t-axis. (displacement can be pos. or neg.) (distance is always pos.).
- To find the acceleration: read the graph!
- To find the change in velocity: find the area between the line and t-axis.
And that my dear friends is some basic Motions & Forces information!
If you are still having trouble in any of these subjects check out the following videos!
or if you would like to test your knowledge try following work sheets and tests!
or if you would like to test your knowledge try following work sheets and tests!
Motion practice:
http://www.nisd.net/taft/classrooms/martin/Physics/Motion/Worksheets/PDFs/numericmotion7-18.pdf
Drawing vectors: http://www.nisd.net/taft/classrooms/martin/Physics/Motion/Worksheets/PDFs/Displacement_DistanceWorksheet.pdf
Friction worksheet:
http://www.neatscience.com/FrictionSheetFromWeb.pdf
Graphs:
http://www.youtube.com/watch?v=pAr0OSnfhaw
http://www.nisd.net/taft/classrooms/martin/Physics/Motion/Worksheets/PDFs/numericmotion7-18.pdf
Drawing vectors: http://www.nisd.net/taft/classrooms/martin/Physics/Motion/Worksheets/PDFs/Displacement_DistanceWorksheet.pdf
Friction worksheet:
http://www.neatscience.com/FrictionSheetFromWeb.pdf
Graphs:
http://www.youtube.com/watch?v=pAr0OSnfhaw