![]() It is possible, but may be difficult for one person to set up these arrangements alone. 6 Hands-On Labs, Inc.ħ Procedure For these next experiments it will be helpful to have an assistant. In SI units, the unit of work is called a Joule (J), and 1 J = 1 N.m. Since work is force (in Newtons) applied over a distance (meters), the units are N.m. Moments are measured in units of Newton-meters. If a lever is not moving, then the sum of all the moments must equal zero. By convention, moments in the clockwise direction are positive and moments in the counterclockwise direction are negative. ![]() As an example: Assuming there is a 2 meter long first-class lever with the fulcrum at 0.5 m and a 12 Newton load weight on one end, how much effort force needs to be applied? F load * d load = F effort * d effort 12N * 0.5 m = F effort * 1.5 m F effort = 6 N.m/ 1.5m F effort = 4 N MA = 12/4 = Hands-On Labs, Inc.Ħ A moment is a force acting at a distance that is producing a torque or twisting effect. Mechanical advantage (MA) is a ratio that shows how much the machine is helping you. You will also calculate moments (defined later). In this experiment you will calculate the mechanical advantage and efficiency of a lever. Examples include tweezers, the human mandible, and the human lower arm (see figures below). In third-class levers, the effort force is located between the fulcrum and the load force. Examples are wheel barrows and nutcrackers. Second-class levers have the load force located between the fulcrum and the effort force. In first-class levers, the fulcrum is located between the effort force and the load force, and examples include the seesaw, scissors, and pliers. 4 Hands-On Labs, Inc.ĥ There are three main classes of levers: first-class, second-class, and third-class levers. Here are important terms regarding levers: Fulcrum = pivot point Force or Resistance = the weight being lifted Force = the pull or push force applied by the operator Distance = the distance the load moves (from the original position), or the distance from the load to the fulcrum Distance = the distance the effort side of the lever moves (from the original position), or the distance from the effort to the fulcrum Work in = Force x Distance Work out = or Resistance Force x Distance D in = effort distance D out = load distance AMA = actual mechanical advantage = load force/effort force IMA = ideal or theoretical mechanical advantage = effort distance/load distance Efficiency = Work out /Work in Neglecting any frictional losses and thinking in terms of conservation of energy we can say that: Work in = Work out, or since Work = Force x distance (W=Fd), one may state: (Fd) in = (Fd) out By applying a small force through a large distance a large force is exerted through a small distance. By changing the position of the fulcrum one can get more power with less effort. Since the sum of torques around a fulcrum is zero (Στ=0), we know that Στ clockwise has to be equal to Στ counterclockwise or the effort force times the effort distance has to be equal to the load force times the load distance. Torque is defined as a force times the lever arm: τ = Fd, and results when force is applied at some distance from an axis of rotation (fulcrum). Levers use torque to gain a mechanical advantage when lifting weights. It consists of a rigid bar which pivots around a fulcrum. A lever is one of the earliest used simple machines used to lift weights. ![]() 3 Hands-On Labs, Inc.Ĥ Discussion and Review In a mechanical sense a machine is any device used to change the magnitude or direction of a force. For an exact listing of materials, refer to the Contents List form included in the LabPaq. ![]() 1 Hands-On Labs, Inc.Ģ Objectives To explore the concept of mechanical advantage using levers 2 Hands-On Labs, Inc.ģ Materials MATERIALS FROM LABEL OR BOX/BAG QTY ITEM DESCRIPTION Student Provides 5 Quarters 1 Meter stick or yardstick 1 Paper cup 1 String 1 Pencil 1 Tape From LabPaq 1 Ruler, Metric 1 Scale-Spring-500-g Note: The packaging and/or materials in this LabPaq may differ slightly from that which is listed above. They will construct first, second, and third class levers using both a ruler and a meter stick, test different loads in the levers, use a spring scale to measure force, and calculate the mechanical advantage of each type of lever. Experiment Summary: Students will learn about the mechanical advantage of machines and how to calculate the efficiency of a machine. Take time to organize the materials you will need and set aside a safe work space in which to complete the exercise. Read the entire exercise before you begin. Version Review the safety materials and wear goggles when working with chemicals. 1 EXPERIMENT Simple Machine Lever Peter Jeschofnig, Ph.D.
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