Gravity and Friction

Gravity & Friction​

By Ms Robinette

Open Ended

What happens when... you throw a ball into the air, knock a spoon off a table or drop a pencil?

Gravity is...

A force of attraction between objects due to their masses.

• Gravity exists between objects even when they are not touching.

• Gravity is a non-contact force.

• It is an attractive force because it always pulls objects toward each other.

​Do you think this dog has ever studied gravity? He sure seems to know that the ball is going to fall - and where it is going to land!

Open Ended

What do you notice about the robot's mass and weight?

Mass vs. Weight

• The amount of matter in an object.

• Constant, will not change.

• Common units of measurement: gram, kilogram, pound

Weight

• The measure of the pull of gravity on that mass.

• A force (usually due to gravity).

• If the force of gravity decreases, weight decreases.

• If the force of gravity increases, weight increases.

• Measured in newtons.

Mass

Multiple Select

A scientific instrument has a mass of 54 kg, and its weight on Earth is about 529 N. Jupiter's gravity is about 2.3 times stronger than Earth's gravity. What is the mass and weight of the instrument on Jupiter?

• Mass: 54 kg

• Mass: 124 kg

• Weight: 529 N

• Weight: 1,216 N

- Your workbook, page 28

"The gravitational force Earth exerts on you is equal to the gravitational force you exert on Earth."

​But we are so much smaller than Earth, so the effect is greater on us. (Earth isn't affected by our gravitational pull, but Earth's gravity keeps us from floating away.)

Fill in the Blanks

Objects near Earth's surface are attracted toward Earth's (center or surface).

Fill in the Blanks

If you dig a hole in Earth's surface and drop an object into the hole, the object will continue to fall until it reaches the (surface or bottom) of the hole.

Open Ended

Imagine you are able to dig a tunnel through the center of Earth to the opposite surface. Describe how gravity would affect you if you jumped into the tunnel. What would happen as you pass the center of Earth?

Every object in the universe attracts every other object with a gravitational force.

The strength of the force depends on two things: mass and distance.

Multiple Choice

If an objects mass decreases, the force of gravity

• increases

• decreases

Multiple Choice

If an objects mass increases, the force of gravity

• increases

• decreases

Multiple Choice

If the distance between two objects increases, the force of gravity

• increases

• decreases

Multiple Choice

If the distance between two objects decreases, the force of gravity

• increases

• decreases

Draw

Draw the force arrows to model each scenario correctly.

Multiple Choice

A metal ball sits motionless on a flat surface. Which of these would make the ball move?

• The force of gravity becomes less.

• The force of gravity becomes greater.

• Two equal horizontal opposing forces act upon the ball.

• Two unequal horizontal opposing forces act upon the ball.

Multiple Choice

What is gravity?

• a contact force

• a frictional force

• a magnetic force

• a noncontact force

Multiple Choice

Which of these is considered a contact force?

• the force between two magnets

• the friction between an object and air

• the gravitational pull of a planet

•      the force between two charged particles

Multiple Choice

Why is the friction force considered to be a contact force?

• Friction affects only solid objects.

• Friction always acts in the same direction.

• Friction is produced when objects slide past one another.

• Friction acts in a direction opposite to the direction of an object’s motion.

Multiple Choice

Which of these describes the gravitational force from a planet?

• large and pulls objects toward itself

• small and pulls objects toward itself

• large and pushes objects away from itself

• small and pushes objects away from itself

Multiple Choice

Which pair of objects has the largest gravitational force?

• marble and car

• marble and baseball

• car and bowling ball

• There is no gravitational force between any of these pairs of objects.