What is a Force Chapter 1, Sec.2

Force is measured in newtons (N)

All forces are exerted by one object on another

Forces don’t always equal motion

Net Force Combining all the forces exerted on an object 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 Subtract forces 12N – 10N = 2N 12N – 10N = 2N

Unbalanced Forces Net force is not zero Net force is not zero Produce a change in motion Produce a change in motion Necessary to cause stationary objects to move 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 Net force is zero Do not produce a change in motion Do not produce a change in motion Do not cause a stationary object to start moving Do not cause a stationary object to start moving

Main forces on an object Gravity Gravity Normal Normal Friction Friction Push/Pull Push/Pull Tension Tension

Gravity Keeps objects on the ground or attracted to the ground Keeps objects on the ground or attracted to the ground

Normal Force Prevents object from “falling into” whatever it is sitting on Prevents object from “falling into” whatever it is sitting on Always perpendicular Always perpendicular

Friction Opposes motion Opposes motion Points away from direction of movement Points away from direction of movement

Push/Pull Physical push or pull Physical push or pull Pushing a crate Pushing a crate Pulling a wagon Pulling a wagon Wind moving a ship Wind moving a ship

Tension Results from a pulling force Results from a pulling force Dragging something with a rope 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)

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An egg is free-falling from a nest in a tree. Neglect air resistance. Diagram the forces acting on the egg as it falls.

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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.

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A skydiver is descending with a constant velocity. Consider air resistance. Diagram the forces acting upon the skydiver.

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A force is applied to the right to drag a sled across loosely-packed snow. Diagram the forces acting upon the sled.

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A car is coasting to the right and slowing down. Diagram the forces acting upon the car.

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