Forces and Motion

Forces and Motion

Part 1

Characterize velocity as having both speed and direction, and describe the position and motion of an object using a frame of reference.

Speed Velocity Acceleration

The distance traveled by an object in a certain time

Ex. 50 MPH

50 Miles Per Hour

​The speed and direction of an object

Ex. 50 m/s north

A vector quantity that is defined as the rate at which an object changes its velocity

1. An airplane travels east with a velocity of 90 m/s. How long does it take the airplane to cover a distance of 405 meters?

T = D / V 405/90 4.5 seconds

2.A boat travels south for 20 minutes and covers a distance of 20 kilometers. What is the velocity of the boat? 
20 minutes is 1/3 of an hour

V = d/t 20/ 1/3 60 km/h south

Finding velocity

All motion is relative to the frame of reference and chosen measurement​

Frame of reference

Multiple Choice

Which statement describes the velocity of a bus traveling along its route?

• The bus travels at an average of 20 mph.

• The bus makes three left turns during its route.

• The bus travels at 20 mph east.

• The bus travels at 20 mph for 30 minutes.

Multiple Choice

Acceleration is the rate of change in an object’s...

• velocity.

• gravity

• force.

• mass.

Multiple Choice

Evelyn drives her car down the road until she comes to a stop sign. She then applies the brakes to stop the car. Which statement best describes what happens next?

• Acceleration no longer exists as the car stops.

• Acceleration decreases velocity until the car stops.

• Acceleration remains constant while friction causes the car to stop.

• Acceleration increases velocity until the car stops.

Multiple Choice

A rider on a bicycle travels north for 1.5 hours and covers a distance of 18 kilometers. What is the velocity of the bicycle?

• 18 km/h.

• 12 km/h north.

• 18 km/h north.

• 12 km/h.

Measured in Newtons

1 N = 1 kg·m/s².

Push or pull acting on an object

are vector quantities because they have magnitude and direction

Direction can cause change in motion

FRICTION FORCE that resists motion between surfaces that are in contact

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FORCES

Applied force: An applied force is a force that is applied to an object by a person or another object. If a person is pushing a desk across the room, then there is an applied force acting upon the object. The applied force is the force exerted on the desk by the person.

​Normal force: The normal force is the support force exerted upon an object that is in contact with another stable object. For example, if a book is resting upon a surface, then the surface is exerting an upward force upon the book in order to support the weight of the book. On occasions, a normal force is exerted horizontally between two objects that are in contact with each other. For instance, if a person leans against a wall, the wall pushes horizontally on the person.

The tension force is the force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends. The tension force is directed along the length of the wire and pulls equally on the objects on the opposite ends of the wire.

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Tension Force

Multiple Choice

A force of 20 N is acting on a box. What other information is needed to accurately describe this force?

• The duration of the force.

• The motion of the box.

• The direction of the force.

• The mass of the box.

Multiple Choice

What is a force?

• A push or pull acting on an object.

• The energy of an object.

• A source of energy in the universe.

• The speed at which an object moves.

Multiple Choice

_______ is a force that resists motion between surfaces that are in contact.

• Resistance

• Friction

• Acceleration

• Inertia

Multiple Choice

An airplane is flying north. What is the direction of the air friction force acting on the plane?

• West.

• East

• North.

• South

Multiple Choice

An apple is on a table. The apple’s mass causes it to push on the table. Which force keeps this push in check?

• The gravitational force acting on the table.

• The normal force exerted on the apple by the table.

• The friction force between the apple and the table.

• The applied force acting on the apple.