Mechanics External L2 Motion

Front 1

Force

Back 1

A push or pull, si unit (N)

Can speed things up/slow down, change direction of object traveling, or change the object's shape

Front 2

How many forces act on an object, what are they?

Back 2

4, thrust, friction, weight and support

Front 3

Forces have both what?

Back 3

A size and direction; a vector

Front 4

If forces are acting in the same direction?

Back 4

Add them together

Front 5

If forces are acting in opposite directions?

Back 5

Subtract larger from smaller force

Front 6

When forces are balanced?

Back 6

There is no net force. If an object is moving, it is moving at a constant speed. If not moving, it'll remain stationary.

Front 7

When forces are unbalanced?

Back 7

There is a net force and object will accelerate or decelerate.

Front 8

How do you calculate Net Force?

Back 8

Use equation:

Fnet=ma

Front 9

Friction

Back 9

A force that occurs when an object moves against another objet, or thru a fluid

Front 10

Does friction oppose movement of an object?

Back 10

Yes, it can act to oppose (prevent or stop) the movement of an object.

Front 11

Can friction cause wear and tear?

Back 11

Thru generation of heat due to friction it can cause wear and tear and slow down objects.

Front 12

Friction transforms into what?

Back 12

Heat energy and sound

Front 13

Another name for friction?

Back 13

Drag, which occurs when an object moves thru a fluid such as air or water.

Front 14

What can reduce effect of friction?

Back 14

If surfaces of the two materials are lubricated (with water or oil etc.).

Front 15

What can increase effect of friction?

Back 15

By making one or more of the surfaces rougher or by pressing them together more strongly.

Front 16

Speed

Back 16

A measure of how far an object can travel in a certain amount of time. A scalar. Si unit (ms-1).

Front 17

To calculate speed?

Back 17

We need 2 variables, distance traveled (m) and time taken to travel that distance (s).

Use equation:

V=∆d/∆t

Front 18

Acceleration

Back 18

The rate at which an object changes its velocity in a certain amount of time. A vector. Si unit (ms-2).

Front 19

Can acceleration be positive and negative?

Back 19

Yes, positive value means speeding up, negative value means slowing down. Negative acceleration is called deceleration, positive named acceleration.

Front 20

To calculate acceleration?

Back 20

Use equation:

A=∆v/∆t

Front 21

Vector

Back 21

Show size/magnitude and direction.

Ie. velocity, displacement, momentum.

Front 22

Scalar

Back 22

Only show a size/magnitude.

Ie. Speed, time.

Front 23

Is d used to represent both distance and displacement?

Back 23

Yes.

Front 24

Is v used for both speed and velocity?

Back 24

Yes.

Front 25

Average Speed/Velocity Equation

Back 25

Vav=∆d/∆t

Front 26

The average speed/velocity equation is useful if?

Back 26

If the object is traveling at a constant speed it velocity, or if an average value is sufficient.

Front 27

Can the average speed/velocity equation be used for instantaneous speeds/velocities?

Back 27

No, there are a separate group of equations for that.

Front 28

If scalar quantities are used, is the answer going to be a scalar and vice versa for vectors?

Back 28

For all equations this is true, yes. Ie. Using displacement and time will give a velocity (a vector quantity) as displacement is also a vector quantity. If using distance and time, result will be speed, (a scalar quantity) as distance is also a scalar quantity.

Front 29

What is the change in velocity equation?

Back 29

∆v=vfinal-vinitial

Front 30

How do you know if acceleration is positive or not with velocity?

Back 30

The sign of the acceleration compared to the sign of the velocity explains if an object is speeding up or slowing down (decelerating).

If velocity and acceleration have the same sign (both +ve or both -ve) then the object is speeding up.

If velocity and acceleration have opposite signs then the object is slowing down.

Front 31

What of direction is not given to the vector acceleration?

Back 31

Following conventions should be used:

Accelerates - Positive Acceleration - Same direction as +ve velocity

Decelerates - Negative Acceleration - Opposite direction to the +ve velocity

Front 32

Distance Graphs

Back 32

Gradient line: (∆d/∆t) gives constant speed of object

Horizontal line: Stationary

Curved upward: Acceleration

Curved downward: Deceleration

The faster the object is traveling, the steeper the gradient/slope.

Distance either increases or stays constant, (it cannot decrease).

Front 33

Displacement/Time Graphs

Back 33

Gradient line: Constant velocity

Horizontal line: Stationary

Curved downward from the left-right:

Accelerating back towards the starting point

Curved upward from left-right:

Decelerating and coming to a stop at the origin.

Gradient of displacement/time graph gives the velocity that the object is traveling.

A positive gradient relates to moving forwards.

A negative gradient means the object is moving in the opposite direction.

Displacement is a vector so direction is important. As the object moves it's displacement can increase, stay constant, or decrease.

Front 34

Speed/Time Graphs

Back 34

Gradient line: constant acceleration

Gradient line downward: constant deceleration

Horizontal line: constant speed

A steep gradient indicates rapid acceleration. Area under the curve gives total distance travelled. Displacement from starting point is unknown as direction cannot be determined with this graph.

Do not illustrate direction. All data points are positive. Graphed line is always above x axis.

Front 35

Velocity/Time Graphs

Back 35

Gradient line: constant acceleration

Gradient line downward: negative acceleration (deceleration)

Horizontal line: constant velocity

Gradient gives the object's acceleration with direction.

Area between graph line and x axis gives object's displacement.

Areas above x axis indicate positive displacement (forward) while areas underneath indicate negative displacements when the object is moving backwards.

Subtracting total areas above the time-axis from the total areas below the time-axis gives the total displacement. A positive result indicates forward displacement. A negative result indicates a negative displacement where the object finishes its motion behind its starting point.

They show direction. Data points above x axis indicate forward motion, below x axis indicate motion in the opposite direction.

Front 36

Acceleration/Time Graphs

Back 36

Because velocity is a vector quantity, a change in direction of a moving object (with or without a change in speed) is also acceleration.

Because we study constant acceleration, graphs will only show vertical or horizontal lines for level 2.

Front 37

When do you use kinematic equations?

Back 37

To calculate instantaneous quantities for distances and velocities when an object is accelerating special equations are required; kinematic equations of motion.

Front 38

Adding Vectors

Back 38

When adding Vectors, the "head-to-tail" rule is used. If vector a must be added to vector b, after drawing vector a, stop. Then start to draw vector b from the arrowhead of vector a. The resultant vector, (C) is drawn from the start (tail) of vector A to the end (head) of vector B.

If vectors aren't in the same or opposite direction, then pythagoras and trigonometry may be used to find the size and direction of the resultant vector if the "head-to-tail" diagram includes a 90° triangle.

When finding the direction of the resultant, we always calculate the angle at the beginning of the resultant arrow or vector inside the vector triangle. We can then explain this angle in relation to North, East, South, or West or as a bearing.

Front 39

Vector Subtraction

Back 39

Change is the the difference between the final and initial quantity, vector Subtraction is used. This can be done by dating the vector addition process. It's achieved by adding the negative of the quantity.

To find the negative vector quantity draw the arrow in the opposite direction.

Use pythagoras and trigonometry to find magnitude and direction of vector C in problems.

Front 40

Relative Velocity

Back 40

Depends upon the motion from the perspective of the observer. The relative Velocity is the difference between two objects/vehicles.

Front 41

Vertical motion under gravity

Back 41

Objects are in "free fall" when object's under influence of gravity and we disregard air friction.

Front 42

When is vertical motion seen as positive acceleration?

Back 42

Such as when an object is falling to Earth, then the acceleration due to gravity can be considered positive.

Front 43

When is vertical motion seen as negative?

Back 43

If an object is thrown upwards, the Acceleration due to gravity slows the objects eventually reversing its direction, this we usually consider this acceleration negative.

Front 44

Horizontal projectile motion

Back 44

Path is called a trajectory. The curved trajectory, ignoring drag or air friction, is caused by the object moving at a constant horizontal velocity, while accelerating downwards due to gravity. The object's vertical velocity decreases decreases as it moves upwards, and increases as it moves downwards. Remember to separate the initial motion into horizontal and vertical components.

Front 45

HPM BALL EXAMPLE

Back 45

At the top of it's path, the vertical instantaneous velocity is zero, but the ball still has it's constant horizontal velocity

Front 46

Does horizontal velocity of projectile change with

Back 46

The vertical component decreases in magnitude as the (ball) rises then decreases as it falls.