Motion

• A change in the position of an object

• Caused by force (a push or pull)

Force• A push or pull on an object• Measured in units called newtons (N)• Measured with a spring scale• Forces act in pairs

Types of Force:– Gravity– Electric– Magnetic– Friction– Centripetal– Normal

Balanced Forces

• When all the forces acting on an object are equal (net force is zero)

• Balanced forces do not cause a change in motion.

• Balanced forces can change the physical properties of an object without changing its motion.

• In your notes, describe an example of a balanced force.

How Can Balanced Forces Affect Objects?

• Cause the shape of an object to change without changing its motion

• Cause an object at rest to stay at rest or an object in motion to stay in motion (inertia)

• Cause an object moving at a constant speed to continue at a constant speed

• In your notes, describe an example of a balanced force affecting an object.

Inertia

• An object at rest will remain at rest until acted upon by an unbalanced force.

• An object in motion will remain in motion until acted upon by an unbalanced force.

• When all forces acting on an object are equal (balanced)

Unbalanced Forces

• When all the forces acting on an object are not equal

• The forces can be in the same direction or in opposite directions.

• Unbalanced forces cause a change in motion.

• In your notes, describe an example of an unbalanced force.

How Can Unbalanced Forces Affect Objects?

• Acceleration is caused by unbalanced forces:– slow down– speed up– stop – start – change direction– change shape

• In your notes, describe an example of an unbalanced force affecting an object.

Net Force

• The total of all forces acting on an object:

– Forces in the same direction are added.• The object will move in the direction of the force.

– Forces in opposite directions are subtracted.• An object will move in the direction of the greater

force.

Calculating Net Force

30 N 10 N

A child was playing with a jack in the box. The lid pushed down with 10 N of force, while the spring pushed up with 30 N of force. What is the net force applied by the spring?

http://commons.wikimedia.org/wiki/File:Jack-in-the-box.jpg

Check Your Answer

30 N 10 N

A child was playing with a jack in the box. The lid pushed down with 10 N of force, while the spring pushed up with 30 N of force. What is the net force applied by the spring?

30 N up - 10 N down = 20 N up

http://commons.wikimedia.org/wiki/File:Jack-in-the-box.jpg

Calculating Net Force

30 N 50 N

Two competitors are playing tug of war. What is the net force? Which direction will the rope accelerate?

Tug of War Game

Check Your Answer

30 N 50 N

Two competitors are playing tug of war. What is the net force? Which direction will the rope accelerate?

50 N to the right – 30 N to the left = 20 N to the right

Tug of War Game

• Draw the box and label the forces.50N 50N

Copy the sentences and fill in the blanks.

1. The forces are ______________.2. The net force is _____________.3. The object will accelerate ______________.

Thursday Warm upNovember 13, 2014

Force and Motion Video

Visual vocabulary

Force and Motion

Aaron Harrell9-14-2010

Force

PUSH

Motion

Speed

Velocity

&

Acceleration

Balanced Forces

Unbalanced Forces

Friday Warm upNovember 14, 2014

• Find the formula for Force on your formula chart and write it down.

• Calculate the force (N) of an object if the mass is 25kg and the acceleration is 2.3 m/s².

Objects affected by unbalanced forces move like…

Objects affected by balanced forces move like…

Mass and Weight• Mass is the amount of stuff (matter) in an object.

– The mass of an object will remain the same anywhere in the universe.– Mass is measured in grams or kilograms.

• Weight is the mass (kg) of an object multiplied by the acceleration of gravity (9.8 m/s2).– The weight of an object depends on the gravitational pull of the

location in the universe.– The gravitational pull on the Moon is only 1/6 of Earth’s gravitational

pull.– Weight is measured in newtons (N).

Mass and Weight

Example: F=ma

A person with a mass of 25 kg x 9.8 m/s2 gravitational acceleration is equal to 245 N of weight force.

F= 25 kg x 9.8 m/s2

F = 245 N

The person exerts 245 N of force on the ground.If the person went to the Moon, they would only weigh 1/6 of 245 N.

Force Force (N) = mass (kg) x acceleration (m/s2)

F ÷

m x a

Force Acceleration (m/s2) = force (N) ÷ mass (kg)

F ÷

m x a

Force Mass (kg) = force (N) ÷ acceleration (m/s2)

F ÷

m x a

PracticeThe acceleration of a sprinter is 10 m/s2. The force exertedon the starting blocks is 650 N. What is the mass of thesprinter?

Force = Mass = Acceleration =

Check Your AnswerThe acceleration of a sprinter is 10 m/s2. The force exerted on the starting blocks is 650 N. What is the mass of the sprinter?

Force = 650 N Mass = 65 kg Acceleration = 10 m/s2

Mass = force ÷ acceleration

Mass = 650 ÷ 10 Mass = 65

PracticeA 56 kg cart is accelerating at 15 m/s2. Calculate the forceexerted on the cart?

Force = Mass = Acceleration =

Check Your AnswerA 56 kg cart is accelerating at 15 m/s2. Calculate the forceexerted on the cart?

Force = 840 N Mass = 56 kg Acceleration = 15 m/s2

Force (N) = mass (kg) x acceleration (m/s2) Force = 56 x 15 Force = 840

PracticeA boat is pulling a 54 kg wake boarder. The force causing the

acceleration is 108N. Calculate the acceleration of the wake boarder.

Force = Mass = Acceleration =

Check Your AnswerA boat is pulling a 54 kg wake boarder. The force causing the

acceleration is 108N. Calculate the acceleration of the wake boarder.

Force = 108 N Mass = 54 kg Acceleration = 2 m/s2