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PPT – Forces at Work PowerPoint presentation | free to download - id: 142ffa-MWFhZ

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Forces at Work

- Speed and Acceleration

Average Speed

- Speed is the distance travelled in a particular

time interval. - The instantaneous speed is the speed at a

specific instant. The cars speedometer records

instantaneous speed.

Australian Mark Webber At the Imola

GP http//www.markwebber.com

An example How long does it take for a car

moving at 90 km/h to travel 230 km

Another way to use the formula is to use a

triangle approach

230

TIME

90

DIST.

- ? Time 230 ? 90
- Time 2.56 hours
- Or 2 hours 33.6 minutes

TIME

SPEED

Ticker Timers

Source www.physicsclassroom.com

Average Speed Vs Instantaneous Speed

Acceleration

- Example Suppose a car accelerates from 60 km/h

to 100 km/h in 5 seconds. Find it acceleration. - Data
- Initial speed 60km/h
- Final speed 100 km/h
- ?change in speed 40 km/h
- Time 5 s.
- Acceleration 40/5
- Acceleration 8 km/h per s.

- Acceleration is the rate at which the moving

object changes speed.

An example How long does it take a car to

accelerate from 4 m/s to 10 m/s if the

acceleration was 3 m/s2

Another way to use the formula is to use a

triangle approach

10-4 6m/s

TIME

Change In speed.

3

- ? Time (10-4) ? 3
- Time 2 s

TIME

Accel.

Forces on a moving car

Normal Force the force the road exerts On the

Car.

Force of Friction

Thrust

Weight of the car on the road

Newtons First Law The Law of Inertia.

- The Law of Inertia.
- An object with no force acting on it remains at

rest or moves with constant velocity in a

straight line.

Newtons Second Law The Force Law.

- The Force Law.
- The acceleration of an object is directly

proportional to the net force on it and inversely

proportional to its mass. - Fma

Newtons Third Law Action-Reaction Law.

- Action-Reaction Law.
- When one object exerts a force on a second

object, the second exerts a force on the first

that is equal in magnitude but opposite in

direction.

Getting Down to Work

- Work is a product of a force and the displacement

of an object in the direction of the force. - W Fd
- Work has the units of Joules
- 1 Joule 1 Newton metre (Nm)
- Work is done on an object only if it moves in the

direction of the force.

Work and Potential Energy

- Potential energy is energy stored in an object

because of its state or position. - The change in potential energy associated with a

particular force when an object is moved form one

point to another to be the work required by some

other (external) force to move the object from

the first point to the second point without

accelerating it.

Gravitational Potential Energy

- Gravitational Potential Energy is the Energy of

an object because of its position. For example,

a person at the top of a waterslide. - GPE mgh
- GPE has units of Joules.

Work - Energy Theorem

- Doing work on an object can increase its kinetic

energy. - The work-energy theorem states that The net work

done on an object equals to its change in kinetic

energy. - Net Work done ?KE

Simple Machines

- All machines, no matter how complex, are made up

of one or more of the six simple machines. The

six simple machines are - Lever
- Wheel and Axle
- Pulley
- Inclined Plane
- Wedge
- Screw

First Class Levers

- In a first-class lever the fulcrum is located at

some point between the effort and resistance

forces. Common examples of first-class levers

include crowbars, scissors, pliers, tin snips and

seesaws

Source http//www.uark.edu/depts/aeedhp/agscience

/simpmach.htm

Second Class Levers

- A second-class lever does not change the

direction of force. When the fulcrum is located

closer to the resistance than to the force, an

increase in force (mechanical advantage) results.

Source http//www.uark.edu/depts/aeedhp/agscience

/simpmach.htm

Pulley Systems

- A pulley is said to be a fixed pulley if it does

not rise or fall with the load being moved. A

fixed pulley changes the direction of a force

however, it does not create a mechanical

advantage.

http//en.wikipedia.org/wiki/Pulleys

Movable Pulleys

- A moveable pulley rises and falls with the load

that is being moved. A single moveable pulley

creates a mechanical advantage however, it does

not change the direction of a force

http//en.wikipedia.org/wiki/Pulleys

More Complex Pulley Systems

http//en.wikipedia.org/wiki/Pulleys

Incline Planes

- The inclined plane makes it easier to move a

weight from a lower to higher elevation.

Simple Machine and Mechanical Advantage

Efficiency of Simple Machines

- The efficiency of a machine is defined as the

ration of output work to input work. The ideal

machine has equal output and input work,

therefore it has 100 efficient.

Gears

- Work equals the product of force and distance,

therefore the small gear is required to run a

longer distance and in the process is able to

exert a larger twisting force or torque, than

would have been the case if the gears were the

same size

Source - http//en.wikipedia.org/wiki/Gears

Gear Ratios

- The gear ratio is the relationship between the

number of teeth on two gears that are meshed or

two sprockets connected with a common chain

The smaller gear has thirteen teeth, while the

second, larger gear has twenty-one teeth. The

gear ratio is therefore 13/21 or 1/1.61

Bicycles Fixed Gears