What is a Force Chapter 1, Sec.2
Net Force • Combining all the forces exerted on an object
Forces in the same direction • Add forces together • 25N + 20N = 45N
Forces in different directions • Subtract forces • 12N – 10N = 2N
Unbalanced Forces • Net force is not zero • Produce a change in motion • Necessary to cause stationary objects to move
Necessary to change the motion of moving objects • Object continues to move when force is removed
Balanced Forces • Net force is zero • Do not produce a change in motion • Do not cause a stationary object to start moving
Main forces on an object • Gravity • Normal • Friction • Push/Pull • Tension
Gravity • Keeps objects on the ground or attracted to the ground
Normal Force • Prevents object from “falling into” whatever it is sitting on • Always perpendicular
Friction • Opposes motion • Points away from direction of movement
Push/Pull • Physical push or pull • Pushing a crate • Pulling a wagon • Wind moving a ship
Tension • Results from a pulling force • Dragging something with a rope
The child next door wants to take his German Shepherd (named Spot) for a ride on his wagon. He chases Spot (who is running away) while dragging his wagon behind him. What forces are acting on the wagon?
Spot, the German Shepherd, is being walked by his best pal, Dot, the Siamese cat. Actually, Dot is pulling Spot across the ice rink, and disturbing the neighborhood hockey game. What are the forces acting on Spot?
A girl is suspended motionless from a bar which hangs from the ceiling by two ropes. Diagram the forces acting on the girl.(hint: the bar is “part of” the girl)
An egg is free-falling from a nest in a tree. Neglect air resistance. Diagram the forces acting on the egg as it falls.
A rightward force is applied to a book in order to move it across a desk. Consider frictional forces. Diagram the forces acting on the book.
A skydiver is descending with a constant velocity. Consider air resistance. Diagram the forces acting upon the skydiver.
A force is applied to the right to drag a sled across loosely-packed snow. Diagram the forces acting upon the sled.
A car is coasting to the right and slowing down. Diagram the forces acting upon the car.