Force and Motion Notes

*AKS : 14c - Define speed as a rate and define velocity as speed in a given direction*

__SPEED__

**MOTION**only takes place when a force has been applied to matter. A**FORCE**is a push or pull- A
**REFERENCE POINT**is generally a stationary object such as a tree, street sign, building etc. - An object is in motion if it changes position over time when compared with a reference point.
**SPEED depends of distance and time**.**The rate at which an object moves is called its SPEED.**- Speed is the distance and object travels in a certain amount of time.
**The SI unit for speed as meters per second m/s.**Other units used to measure speed include:**Kilometers per hour (km/h**), miles per hour (m/h), feet per second (f/s)- The formula to calculate speed is :
**AVERAGE SPEED =**__TOTAL DISTANCE__

**TOTAL TIME**

**DISTANCE = SPEEDx TIME**

**TIME= DISTANCE /SPEED**

Example: If the distance is 100km and it takes a car 2hrs to

travel the distance, what is the speed of the car?

Speed = __Distance__

**Constant Speed**means the speed of an object is not increasing or decreasing, but**remains consistent or the same over time.**

**AKS 14c1 - perform calculations involving speed, time and distance to interpret distance-time graphs as representations of constant velocity or acceleration**

- Distant Time graphs are used show the speed of objects. Time is plotted on the x-axis and distance is plotted on the y-axis. View the examples below.

- High speedLow speed

If an object is not moving, a horizontal line is shown on a distance-time graph. Time is increasing to the right, but its distance does not change. **It is not** **moving. We say it is ****At Rest****.**

If an object is moving at a constant speed, it means it has the same increase in distance in a given time: Time is increasing to the right, and distance is increasing constantly with time. The object moves at a **constant speed**. **Constant speed is shown by straight lines on a graph**.

Two moving objects: Both lines in the graph show that each object moved the same distance, but the steeper dashed line got there before the other one: A **steeper line indicates** a larger distance moved in a given time. In other words, **higher speed**. Both lines are **straight**, so both speeds are **constant**.

*AKS 14c2 – determine the relationship between velocity and acceleration*

__VELOCITY__

- The speed of an object in a particular direction is the object’s
**VELOCITY.** **Velocity changes when the speed or the direction of an object changes.**- An objects velocity is constant only if its speed and direction don’t change.
**Constant velocity is always along a straight line**.**Velocity is expressed in meters per second m/s.**- Velocity must include both speed and direction. Example: An airplane’s velocity is 600km/h south.
- Circle the example of velocity – 25m/s forward, 1500km/h, 55m/h northeast, 70km/h.

__ACCELERATION__

**ACCELERATION**is the rate at which velocity changes.- It is also how fast velocity changes. The faster velocity changes, the greater the acceleration is.
- Acceleration of an object also changes if its speed or its direction changes.
- Anything that’s moving in a straight line( no change in direction) at a constant speed( no change in speed is not accelerating.
**Acceleration is expressed in meters per second per second. (m/s/s)**- To calculate acceleration we use the following formula:

**Acceleration = Final Velocity (V_{2}) - Initial Velocity (V_{1})**

** Time**

- For example: If a car obtains a velocity of 60km/hr in 10seconds, what is its acceleration?

Acceleration = __Final Velocity (V _{2}) - Initial Velocity (V_{1})__

Time

= __60km/hr - 0km/hr __

10sec

= __60km/hr__ = 6km/hr/sec

10sec

**Positive Acceleration**measures a change in velocity of a moving object in which velocity increases or it is speeding up.**Deceleration**is simply negative acceleration. It measures a change in velocity of a moving object that is slowing down. Example when brakes are applied to a car, it is decelerating.**Velocity has direction, so velocity changes if your direction changes. Therefore a change in direction is acceleration, even if there is no change in speed.****CENTRIPETAL ACCELERATION**is acceleration that occurs in a circular motion.**Examples of Acceleration:**

**A braking car (changing speed but not direction)****A car that’s speeding up( why do you think they call that pedal an accelerator)****Your mom’s expensive piece of china that your just dropped(watch it speed up as it falls to the floor)****A dog chasing its tail ( change in direction)****A roller coaster nearing the end of a vertical loop ( change in direction and quite possibly a change in speed)**

Graphs that show acceleration look different from those that show constant speed. The line on this graph is curving upwards. This shows an

**increase in speed**, since the line is getting steeper. In other words, in a given time, the distance the object moves is change (getting larger). It is** accelerating.**

The graph is not a straight line so you can tell you are accelerating. The acceleration is also not constant for each second.

*AKS 14 - investigate the relationship between force, mass and the motion of objects*

*AKS 14a – determine the relationship between force, mass and the motion of objects*

*AKS 14b – demonstrate and explain the effect of balanced and unbalanced forces on an object in terms of gravity, inertia and friction (Newton's Laws of Motion as they pertain to everyday *

*FORCES*

**FORCE**is a push or pull. All forces are exerted on one object by another object.**Force is expressed in newtons (N)****NET FORCE**is the force that results from combining all forces exerted on an object.**BALANCED FORCE**is one in which the net forces equal zero.**There is no motion.**For example: During a tug-of war, if the teams are equal in strength, the forces pulling on both ends of the rope are equal and there is no movement. The forces are balanced with a net force of zero.**UNBALANCED FORCE**has a net force greater than zero. Unbalanced force produces a change in motion. Unbalanced forces cause a non-moving object to start moving.**INERTIA – is the tendency of objects to resist a change in motion.**Inertia is why we wear seat belts. If a car is travelling at 70km/h and comes to a sudden stop, the people inside the car continue moving at 70km/h unless a force prevents their forward motion through the windshield.**The more mass and object has, the more inertia it has and the greater the force it takes to change its motion.****Mass affects inertia.**An object with a large mass has more inertia than an object with a small mass. Changing the motion of an object with a large mass is harder than changing the motion of an object with small mass. Pushing a grocery basket loaded with groceries is harder than pushing it empty. Stopping a train moving at 60km/h also takes longer than a car moving at the same speed because the train has more mass.**Mass is a measure of an object’s inertia.****Small mass = large acceleration****Large mass = small acceleration****Small force = small acceleration****Large Force = large acceleration****FRICTION**is a force that opposes the motion of an object. Friction opposes motion when two surfaces are touching. The contact reduces the speed of the moving object and releases heat.**Rougher surfaces create more friction.****Greater forces create more friction.**The amount of friction depends on the force pushing the surfaces together. If force is increased, friction between the surfaces also increases.

**TYPES OF FRICTION **

**Sliding Friction -**Sliding friction is when two solid surfaces slide against each other. Putting a book flat on a desk and moving it around is an example of sliding friction.**Rolling Friction -**A force which opposes the motion of any object which is rolling over the surface of another. Example anything on wheels – roller skates, cars, trains, planes**Fluid Friction -**Fluid friction is the friction between a solid object as it moves through a liquid or a gas. Example swimming, a fast moving car through the air.**Static Friction -**Friction between two objects in contact that are not moving.

**REDUCING FRICTION**

- Use Lubricants – motor oil, grease, oil, wax, (gas lubricant comes out of the tiny holes on an air hockey table)
- Switch from sliding to rolling friction. ( ball bearing are places inside the wheels of inline skates and bicycles to make it easier for the wheels to turn)

**INCREASING FRICTION**

- Make the surface rougher. ( We added sand to the icy streets to keeps the cars from skidding)
- Increase the force pushing the surfaces together. (Place a heavy rock on the newspaper on the park bench so that it will not be blown away.)
- is the amount of mater in an object and its value does not change. It is constant.