Situations of Force (7.7A)
Overview
Student Expectation
The student is expected to contrast situations where work is done with different amounts of force to situations where no work is done such as moving a box with a ramp and without a ramp, or standing still
Key Concepts
· Key Concept 1: Work is performed when a force causes an object to move. If an object does not move, no work is done upon that object.
· Key Concept 2: Work is calculated by multiplying the force exerted on an object by the distance it moves in the direction of the force (W=fd).
· Key Concept 3: Ramps, or inclined planes and other simple machines can reduce the amount of work force needed to move an object, but they do not change the amount of work done. When the force is reduced, the distance is increased, so that the amount of work done remains the same.
· Key Concept 4: Friction is a force that interacts between an object and its surface and acts as an additional force that needs to be overcome to move an object.
Objective:
7.7A Contrast situations where work is done with different amounts of force to situations where no work is done such as moving a box with a ramp and without a ramp, or standing still.
Foundation:
Work might happen when an object moves a certain distance under force. Work here means mechanical work, and it is measured in units called joules. It is a scalar quantity and represents how much energy transfer occurs while the object is moving. The value of work, which is also measured in joules, is equal to force multiplied by distance. Note that the force and distance here have to be in the same directions. That is, the force should be decomposed into the direction in which the object moves.
Work is linked with certain quantity of energy change, and does not change based on how the work is finished. For example, there are different ways to accomplish work, such as making use of inclined planes, ramps or simple machines. However, when the force required is reduced by these versatile methods, the other factor in the Work formula, distance, does increase. Thus the total amount of energy or work remains the same.
Friction happens between the contacting surface and a moving object. This acts as a resister to prevent the relative motion between the surface and the object. When we move an object, the direction of this friction force is opposite to the direction where we push the object. Hence this resisting force needs to be overcome in order to successfully move the object. Forces affect motion. There are lots of examples you may already notice in your daily life. The process of seedling growth demonstrates a greater upward force than the gravity, which is working in the opposite direction. This is the reason that the plants can break through the soil.
Work: The use of force to move an object through a distance W=Fd
Mass: The amount of matter in an object or substance
Distance: Measurement from one place to another
Friction: Force that opposes the sliding motion between two touching surfaces
Simple Machines: Devices that reduce the amount of force needed, but do not reduce the amount of work being done
Inclined Plane (Ramp): A simple machine that is sloping at a particular angle
Balanced Forces: Force on an object that does not change the motion of the object
Unbalanced Forces: Force on an object that cause change in the motion of the object
Force: A push or pull that changes the motion or position of an object
Net Force: The sum of all the forces acting on an object
Motion: A change in an object’s position, direction, or location
Turgor Pressure: Pressure of water molecules against the cell wall that allows plants to stand up straight
Geotropism (Gravitropism): A plant’s growth in response to the force exerted upon them by gravity