## Mouse Trap Vehicle: Finding Friction

**28, 2012**

Earth shattering secrets for building record setting and winning mousetrap cars and racers. Here you will find all the latest and greatest untold construction secrets so you can build your very own mousetrap vehicle.

#### Purpose

To determine the force of friction against a mousetrap vehicle.

#### Equipment Needed

- Starting Energy (From the lab: Energy of a Mouse Trap)
- Meter Tape

#### Discussion

Mousetrap powered vehicles convert their starting potential energy into work. The work that is done is used to overcome the force of friction acting against the vehicle's motion. In most cases the friction is the greatest at the vehicle's bearings (where that axle comes in contact with the frame). All objects that move through the Earth's atmosphere will experience air resistance but for the purpose of this activity you will ignore this force. The total amount of work done will be equal to the total amount of starting potential energy of the mouse trap; this number must be first calculated from that activity *Energy of a Mouse Trap*. The predicted travel distance is equal to the starting energy divided by the force of rolling friction. You should observe (by comparing your results to other students' results) that the less rolling friction a mousetrap car has the greater the travel distance of the vehicle.

W = F × d

**formula 1**: work [w] is defined in the mathematical terms as a force [f] applied through a distance [d]. This equation is only good for a constant force. Work is measured in joules, force in newtons, and distance in meters.

PE = f_{total} * d_{ travel}

**formula 2**: potential energy (PE) is equal to the work done or the energy needed to overcome the total friction (f total) through the travel distance (d travel).

d_{ travel} = PE / f_{total}

**formula 3**: the total travel distance (d travel) of a mousetrap powered vehicle is equal to the starting energy (PE) divided by the total of friction (f total) acting against the vehicle's motion.

ƒ = μN

**formula 4**: The force of friction [ƒ] depends on how slippery two surfaces are together called the coefficient of friction [μ] and how hard the surfaces are pressed together [N]. The coefficient is measured in newtons, the normal force in newtons, and the coefficient is newtons over newtons.

N = mg

**formula 5**: The normal force (N) is how hard two surfaces are pressed together or the weight of the object. This means that the normal force (N) is equal to the weight of the car or the mass (m) of the car times the acceleration of gravity (g).

### Step 1:

Wind-up and release your mousetrap vehicle. Measure the total travel distance from the start to the finish line. Test your vehicle several times and then calculate the average travel distance for your vehicle.

Travel Distance = _____ meters

**travel distance**: measure the maximum travel distance.

### Step 2:

Calculate the total friction from the average travel distance using the following formula:

f_{total} = PE / d_{ travel}

**rolling friction**: the rolling friction (f rf) of a mousetrap powered vehicle is equal to the starting energy (PE) divided by the travel distance (d travel).

total friction = _____ N

### Step 3:

Find the mass of the vehicle's frame. It is only the weight of the frame that rests on the bearings and presses the axles and bearings together; therefore, you must remove the wheels and mass only the frame.

mass of frame = _____ kg

**mass of frame**: find the mass of the frame without the wheels

### Step 4:

Calculate the weight of the frame the following formula by multiplying the mass of the frame by the acceleration of gravity.

N = m × g

**weight**: the weight [N] is equal to the mass [m] of the frame multiplied by the acceleration of gravity [g]. The acceleration of gravity is equal to 9.8 m/s/s.

weight of frame = _____ N

### Step 5:

Calculate the coefficient of friction from the following formula.

μ = f_{total} / N

coefficient of friction = _____ N/N

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