Science Grade 4 - Chapter 4.1 - Forces

Is friction helpful or not helpful in the examples below? Choose the answer

b. slowing down the moving parts of a machine:

• helpful

• not helpful

Is friction helpful or not helpful in the examples below? Choose the answer.

a. moving a box on rough floor

• helpful

• not helpful

Is friction helpful or not helpful in the examples below? Choose the answer.

c. preventing slipping on a smooth floor:

• helpful

• not helpful

Parts of an engine move against each other, which creates a force between them. This force slows down the motion of these parts causing the engine to heat up and get damaged.

a. What the name of this force? Choose the answer.

• Push

• Air resistance

• Friction

• Gravity

Answer explanation

Friction - The force between two objects that are touching each other.

Parts of an engine move against each other, which creates a force between them. This force slows down the motion of these parts causing the engine to heat up and get damaged.

b. Certain substances can be used to reduce the effect of this force. What are these substances called? Choose the answer.

• magnets

• Particles

• Lubricants

• Matter

Answer explanation

A lubricant is a substance that helps to reduce friction between surfaces

Parts of an engine move against each other, which creates a force between them. This force slows down the motion of these parts causing the engine to heat up and get damaged.

c. Which substance can be used in this case? Choose the answer.

• Water

• Air

• Oil

• Nitrogen

Which force slows down objects moving through air? Choose the answer.

• Air resistance

• Gravity

• Friction

Answer explanation

Alan Eustace's jump was recorded from the height of 135,889 feet (41.41 kilometers), making his the highest jump ever, topping even the red bull highest skydive. HE WAS JUMPING FROM SPACE!!!!!!

Which touching surfaces produce the most friction when moving against each other? Choose the answer.

• A plastic sledge on snow

• two pieces of smooth plastic

• a box on a smooth floor

• a box on a cement floor

Answer explanation

Rough surfaces like cement and grass create more friction than smooth surfaces.

A push or a pull is a ______________.

Answer explanation

A force is a push or a pull.

Fill in the blanks using words from the box below.

As an object moves through air, it bumps into the air particles, which ___________ its movement. An object with a _____________ surface bumps into more air particles as it moves through air.

• larger

• smaller

• accelerates

• slows

Answer explanation

As an object moves through air, it bumps into the air particles, which slows its movement. An object with a larger surface bumps into more air particles as it moves through air.