Mousetrap Cars Kristin McCoy - PowerPoint Presentation

Slide1

Mousetrap Cars

Kristin McCoy

Academic Coordinator, CSU Fresno MESASlide2

What is a Mousetrap Car?

Vehicle powered by the spring device of a mousetrap

Mousetrap is a simple machine – uses mechanical advantage to multiply forces

Mousetrap acts as a third-class lever with the spring as the fulcrum and the hammer as the loadSlide3

Third Class Lever

Resultant force (load)

Applied Force

Resultant Force (Load)

Fulcrum

Applied Force

A

fulcrum

is the point or support on 

which a lever turns.Slide4

What is a Mousetrap Car?

How does the power source work?

The spring propels the hammer, which causes an enormous release of energy (

Kinetic

)

The hammer is connected to a string that is wound around the

drive axleThe string unwinds as the hammer snaps – making the car roll!!Slide5

Scientific Concepts

Important concepts for building a mousetrap car to consider:

Potential Energy

Kinetic Energy

Force

Friction

TorquePowerSlide6

Scientific Concepts

Potential Energy:

Energy that is stored within an object, not in motion but capable of becoming active

Have stored potential energy (in the spring) when your mousetrap is set and ready to be released.Slide7

Kinetic Energy:

Energy that a body possesses as a result of its motion

Potential energy becomes kinetic energy as the mousetrap car begins to move

Some of this energy goes to friction – the rest makes the car goSlide8

Force:

An action that causes a mass to accelerate

To change the motion of your mousetrap car, a force must be applied.

To increase the acceleration of the car, the force must be increased or the mass decreased (Newton’s Second Law)Slide9

Friction:

The force that opposes the relative motion of two surfaces in contact

Friction will slow- and eventually stop – the mousetrap car

Friction occurs between the wheels and the floor and between the axle and the chassisSlide10

Torque:

Can informally be thought of as “rotational force” or “angular force” that causes a change in rotational motion

In the mouse trap car the snapper arm applies a force to the drive axle through the pulling string. This in turn causes a torque to be produced around the drive axle.Slide11
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Power

Rate at which work is done or energy is used

In the mousetrap car, the same overall amount of energy is used regardless of its speed – only the rate of use changes

distance

– to use energy slowly

power

– use it more quickly ( lots of energy needed at the start to get car moving up a ramp)Accuracy – balance is important (enough power to reach target, but not a lot of energy saved for the end so braking will be easier)Slide13

Construction Hints!!

When building a mousetrap car, there are a number of variables to consider:

Weight of car

Placement of mousetrap

Length of the snapper arm and the string

Size and type of wheels

Wheel-to-axle ratioDepends on the goal of the car – distance, accuracy, or powerSlide14

Weight of the Car

Build the lightest possible vehicle

Lighter will require less force to begin moving and will experience less friction than heavier cars

If a car is too light, it will not have enough traction

This causes the wheels to spin out as soon as the trap is releasedSlide15

Length of the Snapper Arm

and The String

Long snapper arms and short snapper arms release the same amount of energy

The difference is in the rate at which the energy is released (power output)Slide16

Distance

try long arm. This will provide less force, but more distance

Accuracy

try shorter arm. This will provide more force and power output, but less distance

Power

try a shorter arm. Will provide more force and power output, but less distance.

These cars need power to get up a rampSlide17
Slide18

For all cars, the lever arm should just reach the drive axle when its in the ready position

When the string is wound, the place where the string is attached to the snapper arm should be above the drive axle

This maximizes torque as the car takes off (max torque occurs when you lever arm and string form a 90⁰ angle)Slide19

For all Cars

Lever arm should just reach drive axle when in ready position

When string is wound, place string to the snapper arm above the drive axle

This will maximize torque – max torque occurs when lever arm and string form a 90°angleSlide20

Correct Length: lever arm just reaches axle. Lever arm and string form a 90°angle, allowing for max torqueSlide21

For Distance and Power Cars:

String length shorter than distance from leer arm to drive axle when the trap is in relaxed position

Allows string to release from hook preventing tanglesSlide22

Accuracy Cars:

String serve as a braking mechanism – string length is very important and must be

exact.

String can be tied to drive axle so when string runs out, car will come to a sudden stop

String length can be set so that it runs out exactly when car reaches the target Slide23

All cars:

if wheels are misaligned, car will be working against itself – energy will be lost

Most visible sense, misaligned wheels also mean care won’t go in desired direction

Power cars:

Misaligned can cause car to leave ramp

Accuracy cars:

Misalignment can cause car to miss target

** string tension can also cause misalignmentSlide24

Wheel-to-Axle Ratio

Power cars:

Smaller wheel-to-axle ratio best

Increasing size of axle will decrease wheel-to-axle ratio

This will increase torque giving more pulling force for every turn of the wheelSlide25

Placement of Mousetrap

Distance Cars:

Place trap farther from drive axle

Accuracy Cars:

Placement of mousetrap depends most on the length of the string

Power Cars:

Place trap closer to the drive axle – get more pulling forceSlide26

Size and type of Wheels

For Accuracy Power:

Make sure wheels have good traction

Traction is a good type of friction

Increase traction by covering edges of the wheel with a rubber band or middle of a balloon

Accuracy:

Traction will be important ensuring the car can come to a sudden and accurate stop without skidding