You will need

- - dynamometer;
- - table of coefficients of friction;
- calculator;
- - Libra.

Instruction

1

Find the resistance force, which acts on a uniformly rectilinearly moving body. For this dynamometer or another method to measure the force that must be applied to the body to move uniformly and rectilinearly. According to Newton's third law it will be numerically equal to the force of resistance to movement of the body.

2

Determine the resistance force of the body that moves along a horizontal surface. In this case, the friction force is directly proportional to the reaction force bearing, which in turn is equal to the force of gravity acting on the body. Therefore, the resistance force in this case or Fтр the friction force equals the mass m of a body measured weights in kilograms, the acceleration of gravity g≈9.8 m/S2 and the coefficient of proportionality μ, Fтр=μ∙m∙g. The number μ is called the coefficient of friction depends on the surfaces that make contact when moving. For example, for friction of steel on wood this coefficient is equal to 0.5.

3

Calculate the resistance force of a body moving on an inclined plane. In addition to the coefficient of friction µ, mass of the body m and the gravitational acceleration g, it depends on the angle of inclination of the plane to the horizon α. To find the resistance force in this case, you need to find the product of the friction coefficient, body mass, gravitational acceleration and the cosine of the angle at which the plane is inclined to the horizon Fтр=μ∙m∙g∙cos(α).

4

When the body moves in the air at low speeds the resistance force FC is directly proportional to the speed of the body v, Fc=α∙V. The factor α depends on the properties of the body and viscosity of the fluid and is calculated separately. When driving at high speeds, for example, when the body falling from a considerable height or the vehicle is moving, the resistance force is directly proportional to the square of the velocity Fc=β∙v2. Additionally, the coefficient β is calculated for high speeds.

# Advice 2 : How to find force of air resistance

To determine the

**force****of resistance***of air*create the conditions in which the body begins under the action of gravity to move uniformly. Calculate the value of gravity, it is equal to the force of air resistance. If the body moves in the air, picking up speed, the force of his resistance is by using Newton's laws, the force of air resistance can be found from the law of conservation of mechanical energy and special aerodynamic formulas.You will need

- rangefinder, scale, speedometer or radar, ruler, stopwatch.

Instruction

1

The definition of air resistance a falling body uniformly Measure body weight using a scale. Dropping it from some height, make sure it is moving evenly. Multiply body weight in kg by the acceleration due to gravity, (9.81 m/S2), the result is the force of gravity acting on the body. And since it moves uniformly and rectilinearly, gravity will be equal to the force of air resistance.

2

The definition of air resistance the body will skorostrel gaining body mass by using weights. After the body began to move, using a speedometer or radar measure its instantaneous initial velocity. In the end, measure its instantaneous final velocity. Speed is measure in metres per second. If you measure it in kilometers per hour, divide the value by 3.6. In parallel to using the stopwatch to measure the time in which occurred the change. Subtracting the final speed from the start and dividing the result by the time, find the acceleration with which the body moves. Then find the force that causes a body to change velocity. If the body falls, then it is gravity, if the body moves horizontally, the thrust of the engine. From this power subtract the weight of a body on its acceleration (Fc=F+m•a). This will be the force of air resistance. It is important that the body did not touch the ground, for example, moving on an air cushion or fallen down.

3

Determination of air resistance to a body falling from vicotiasecret body weight and drop it from a height, which is known in advance. Upon contact with the surface of the earth clamp the velocity of the body using a speedometer or radar. Then find the product of the gravitational acceleration 9.81 m/S2 on the height from which the falling body, subtract from this value the speed squared. The result, multiply by body weight and divide by the height from which it fell (Fc=m•(9,81•H-v2)/H). This will be the force of air resistance.

Useful advice

In the General case the resistance force can be found if the density of the air multiplied by the square of the velocity with which the body moves, divide this value by 2 and multiplied by the cross-sectional area of the body perpendicular to the direction of the velocity. The result must be multiplied by the aerodynamic coefficient, which is determined experimentally. Therefore, the application of this formula difficult.