Answers to AQA GCSE Upthrust

Practice Questions

1. State the definition of upthrust

Upthrust is an upward force on an object that a fluid exerts 

2. Describe how pressure changes with depth of liquid.

As depth increases, pressure increases

3. Explain how an upthrust force is formed on a beach ball that is  submerged in the water.

The bottom of the beach ball is at a greater depth of water than the top of the beach ball. So, there will be a higher pressure on the bottom of the beach ball, than the top. 

As pressure is the force per unit area, it means that the bottom of the ball experiences a greater force than the top. So, the resultant of these two forces is the upthrust.

The resultant force formed will be upthrust.

4. Delete the two incorrect words in the brackets to make the following sentence correct: 

For an object to float its weight must be (equal) the upthrust of water.

less than and greater than deleted

5. Explain why an object that is less dense than water will float on the surface of water. 

As the object is less dense than water, the object’s weight will be less than the weight of the water displaced. Therefore the weight of the object is less than the upthrust of the liquid. So, it floats.