Today we will: Learn what “work” is! Learn how to calculate work Learn what Power is!

Work In physics, work is the amount of energy transformed (changed) when a force moves an object (in the direction of the force)

What is WORK Work is done when a force causes an object to move in the direction that the force is applied. If there is no movement, there is no work =

Calculating work The amount of work done (measured in Joules) is equal to the force used (Newtons) multiplied by the distance the force has moved (meters). Force (N) Distance travelled (m)

Two things must happen for work to be done. What are they? •A force must be applied to an object. •The object must move in the same direction as the force.

Important The force has to be in the direction of movement. Carrying the shopping home is not work in physics!

Is it work? A scientist delivers a speech to an audience of his peers. A body builder lifts 350 pounds above his head. A mother carries her baby from room to room. A father pushes a baby in a carriage. A woman carries a 20 kg grocery bag to her car.

Work (J)= Force(N) x distance(m) W = Fdcosθ

Work = Fdcosθ What if the force is at an angle to the distance moved?

Work done (J) = Force (N) x distance (m) A woman pushes a car with a force of 400 N at an angle of 10° to the horizontal for a distance of 15m. How much work has she done?

Positive or negative? d F F d d F F d Positive Work: Works with the motion Negative Work: Works against the motion

Lifting objects When we lift objects, we are doing work because a force is moving. Force Distance moved

Lifting objects Our lifting force is equal to the weight of the object. Lifting force weight

Work done (J) = Force (N) x distance (m) A woman pushes a car with a force of 400 N at an angle of 10° to the horizontal for a distance of 15m. How much work has she done? W=Fdcosθ=400x15xcos(10)=400x15x0.985 W = 5908 J

Work done (J) = Force (N) x distance (m) A man lifts a mass of 120 kg to a height of 2.5m. How much work did he do?

Work done (J) = Force (N) x distance (m) A man lifts a mass of 120 kg to a height of 2.5m. How much work did he do? Force=weight=mg=120x10=1200N Work = F x d = 1200 x 2.5 Work = 3000 J

Practice Problem Julie is walking her dog Barney. She holds the leash at a 40 degree angle to the ground. How much work does Julie do when she applies a 35 N force on the leash as Barney sees a squirrel and drags her 11 m? 294 Nm

Power! The amount of energy transformed (changed) per second. Rate of work done. It is measured in Watts 1 Watt = 1 J/s  

Power  

Measuring your work Name Mass (kg) Force (N) Distance (m) Work of one lift (J) # of lifts in 1 min Total work (J)

Work done in stretching a spring Work done in strectching spring = area under graph F/N x/m