FORCES AND MOTION

HOW DO FORCES AFFECT OBJECTS?

• Force- a push of pull that one object

exerts on another.

• Forces can change the motion of the

object.

• A baseball batter uses force to hit the ball

and that hit changes the direction of the

ball.

• Forces can also change the shape of

objects.

• You use force to crush a soda can.

HOW DO YOU MEASURE FORCES?

• To measure force we use a spring scale.

• Measured in Newtons

• Friction- a force that opposes the

motion of the object sliding over

another.

• If you pull an object with a spring scale

along a surface, you can feel the object

resist the sliding.

WHAT ARE THE TYPES OF FRICTION?

• Friction acts anytime the surfaces of

objects are in contact.

• 3 kinds of friction:

• Sliding Friction: When opposite forces push

across.

• Static Friction: Prevents the start of any

movement between surfaces in contact. If the

surface is smother or steeper, there might not

be enough to hold an object in place.

• Rolling Friction: Friction allows wheels to move

us forward. Friction between wheels and the

ground push an object ahead.

HOW DO DRAG FORCES ACT?

• Drag Motion- when an object moves

through a gas, like air, or any liquid, there

is a force that opposes motion.

• The object moves through air, the air

molecules bump into it, which causes the

object to slow down.

• Similar to sliding friction because they both

oppose motion.

• Drag force depends on speed, size, and

shape.

• Speed: the faster the speed the greater the

drag.

HOW DO OBJECTS ATTRACT?

• Gravity- a force of attraction that occurs between

any object that has mass.

• Gravity is a force that only pulls.

• The larger the mass of an object, the more

gravitational pull it has.

• The Earth’s gravity is much larger than a person’s, so we

can feel the gravity of the Earth more than we can feel

the gravitational pull of others.

WHAT AFFECTS GRAVITY?

• The force of gravity between two objects

depends both on the masses of the two objects

and the distance between the objects.

• The closer the objects are to each other, the

stronger the force of gravity they exert on each

other.

• Weight- is the force of gravity between the

Earth and the object.

• Weight is measured on a scale.

• Each planet pulls on an object’s mass differently

which affects its weight.

WHAT ARE BALANCED FORCES?

• Net Force- combined effect of the

forces acting on an object.

• When the forces acting on an object are

equal the net force is 0 and the object

doesn’t move.

• Anytime two or more forces completely

offset one another, we say they are

balanced forces.

• When the forces on an object are

balanced, the net force on the object is

zero.

WHAT ARE UNBALANCED FORCES?

• Unbalanced forces- When the force or forces

acting on an object do not completely offset one

another.

• The leftover force can be represented as a single

push of pull in a certain strength and direction.

• When a net force is unbalanced, it means the net

force is not at zero.

WHAT IS NEWTON’S FIRST LAW?

• Newton’s First Law of Motion- “An

object in motion tends to stay in motion,

and an object at rest tends to stay at

rest.”

• An object’s velocity can only be

changed by applying a force to it.

• Motion can only be changed by

applying a force.

• Inertia- the tendency of an object to

oppose any change in motion.

HOW DOES INERTIA AFFECT YOU?

• Jolting forward when a bus stops quickly

is only one way you tend to keep moving

because of inertia.

• Inertia is why seatbelts are so important.

• You might be able to control yourself in a car

when you know it is going to make a turn, it is

almost impossible to control your movement in

a car that suddenly stops or changes

direction.

• Seatbelts keep you moving with the car or

stop you from moving when the driver breaks.

WHAT MAKES OBJECTS TRAVEL IN A CIRCLE?

• An object that is traveling in a circle is

accelerating even if it moves at a steady

speed.

• It accelerates because its direction of travel is

constantly changing.

• The pull of a string keeps the object

moving.

• Once the string breaks, there will no longer

be any unbalanced force on the object. Its

inertia will carry it straight ahead at a

constant speed.