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Lab Report Friction

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Hypothesis: For an increase in a normal force, there will be a corresponding increase in friction.

Introduction: Force is usually connected with a push or pull exerted on an object. In this experiment, I am using a contact force, a force that exists from physical contact between two things. I am pulling the spring scale, which measure force in Newtons (kg x m/s2), and then the block is moving. Different masses (kg), or the measure of the resistance of an object to changes in its motion due to a force, of an object have different accelerations (∆v/∆t). The more massive the object is, the smaller its acceleration. Newton's third law of force says that if two object interact, the force F12 exerted by object 1 on object 2 is equal and opposite to the force F21 exerted by object 2 on object 1. The action force, F12, and the reaction force, F21, act on different objects.

Illustration 1) Action/Reaction Forces Act on Different Objects

If a bucket is at rest on a table, the action force is the force of the Earth on the bucket, and the reaction force is force exerted by the bucket on the Earth. The bucket does not accelerate downward, because it is held up by the table. The table, therefore, exerts on the bucket and upward force N called the normal force. We define it the normal force because it is normal, or perpendicular to the table's surface.

Illustration 2) Normal Force

If an object is sliding horizontally, it faces the forces of friction. Friction is the resistance to the motion of an object because of the object's interaction with its surroundings. Newton's second law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. If you try to drag a block of wood across a table, the initial force before the block begins to move is the force of static friction. Eventually, as we increase the pull, the force of static friction reaches its max, and the block begins to move. The force of friction for an object in motion is the force of kinetic friction. When we want to find the magnitude of the force of kinetic friction acting between two surfaces, we find Ff=kThe k is the dimensionless/unit less coefficient of kinetic force. The normal force (N) equals the weight of the object in Newtons. We use the formula W=mg or Weight=mass in kg x acceleration due to gravity for weight as well as force (Ff).

Ex. 1)

Procedure: See lab book.


Surface Weight Trial Ff  N (normal force in Newtons)

Table 605 g 1 1.6 N .27 5.9 N



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