Electrical Hazards: Dangers of Improper Usage

Electric shock:

When used inappropriately, electric shock can result and cause serious injury. Explosion and fire caused by electrical sparks, short circuits or overload heating in the presence of flammable material can occur. Parent or teacher supervision is required and was present during the use of electrically powered equipment (electric drill and freezer) in this experiment. Plugs that were cracked or broken were not used.

The cable was checked to ensure it was in good condition and free from breaks in the insulation.

The cable was not run across the floor in order to prevent a tripping hazard. The equipment was checked for faults before use. The operator and supervisor were aware of the mains switch so that power could be turned off in an emergency. Electrical equipment was not used in the vicinity of flammable or explosive material or any where it may get wet.

Burns:

The electrical drill contains very hot moving parts which can cause burns and other serious injury.

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 Safe use of the electrical equipment was demonstrated by the parent before use. The electric drill was held by a steady hand and fingers were kept clear of the moving parts. The drill was turned off after use, and left to cool down in safe area. Cuts and infection from sharp objects: The coping saw, can opener and the edges of the tin cans are sharp and can result in injury and infection.

Parental supervision was present during the use of the coping saw and the can opener.

To avoid cuts from the coping saw, the dowel was fixed in a vice and fingers were kept well clear of the saw. Special care was taken when opening the tin cans and when testing the tin cans. If cuts did result, the wound and the object must be washed thoroughly with antiseptic to avoid infection. Injury from heavy and large objects: The board used for the incline was large and relatively heavy. It can cause injury when dropped or when making contact with another individual. Experimentation was commenced outside to avoid working nearby other people. Two students carried either end of the board to avoid dropping it and avoid hitting other students. Leather shoes were worn throughout the investigation.

Injury from loose objects:

The objects used in races can be lost on the ground where they pose a risk to someone who might step on them. A large plank was positioned at the end of the incline to stop the objects when they reach the end and to avoid them rolling onto the floor. When the objects are not being used, they were kept in a box. Sunburn: Experimentation was done outside to avoid risk to nearby students.

However, sun burn can result from being outside to long. Appropriate sun protection was worn throughout the investigation: sunscreen, hat and suitable clothing.

The time it took for the object being raced to go from the start line to end was measured. Two timers took measurements for the five times the object was rolled down. These times were then averaged. All this raw data collected is displayed in Appendix 1. Also included in Appendix 1 is the independent, dependent and controlled variables for each race, pictures of the objects being raced, and the measurements of the objects.

Overview of the calculations

Determining the theoretical final linear velocity of the object: We know that the final velocity is given by: Because it is not dependent on time, this will give the theoretical value an object should role down. In this particular race, the h at which the object was released is 295.2mm or 0.2952m. We also know that the objects used in this race were solid cylinders, we know that I = 1/2 MR2.

Letting acceleration due to gravity be 9.81ms2, the theoretical final velocity for the objects in race A is: This procedure can be carried out for all objects in the other races for which we already know their moment of inertia. In the case of the objects in race F and race G, their moments of inertia are unknown so we got nothing to compare them to.

Determining the measured final linear velocity of the object:

We also know from our introduction that average linear velocity is given by: where, vo and vf is the initial and final velocities respectively. When the object being rolled down the incline is at the top, being held in its place by the ruler, it has zero velocity.

Therefore in this case:

Keeping in mind that vav also equals: where s is the distance traveled and time is the time taken to travel this distance, we can combine these two equations and rearrange them to get the expression: By substituting measured values of s and t, this will provide the measured value of the objects final linear velocity.

For example, take the object filled with wet sand, which traveled 1.7m in an average time of 1.83 seconds. Hence its final linear velocity is: The measured final velocities of the other objects can be calculated in a similar fashion. The calculations are summarised below. Note once again, this procedure can be carried out for all other objects in the races. Determining the theoretical linear acceleration of the object: In the introduction, we determined that the theoretical linear accelerations for objects of various shapes rolling down an incline. The general equation for any object was found, and is given by: Once again, let's determine the theoretical acceleration for the object in race A filled with wet sand.

Determining the measured linear acceleration of the object:

From the above steps, we know that the measured linear final velocity is 1.95ms-1 for the object with wet sand in it. Since the initial velocity of the objects is zero, we can determine the measured final linear acceleration by dividing the final velocity by time. The above processors for determining the theoretical and measured linear accelerations can be continued for all the objects deemed necessary.

Checking the conservation of mechanical energy in rolling motion:

We know that at the top of the incline, all the objects being raced had zero velocity. Hence, they possessed only gravitational potential energy. At the bottom of the incline, the objects possess no gravitational potential energy, which has been converted into rotational and translational kinetic energy. To check that the mechanical energy has been conserved, the potential energy at the top should equal the total kinetic energy at the bottom.