How to find the resistance force

At any movement between the surfaces of the bodies or in the environment in which it moves, there are always forces of resistance. They are called frictional forces. They can vary the friction surfaces, the support reactions of the body and its speed if the body moves in a viscous medium, for example water or air.

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.