Friction, air resistance, water resistance and upthrust
This Topic is About...
- I will find out about different forces like upthrust, friction, air resistance, and water resistance.
- I will learn that objects can have more than one force acting on them at the same time.
- I will use diagrams to show the direction and name of forces acting on an object.
- I will predict and test which parachute design will fall the fastest.
- I will measure carefully and record my results in a table.
- I will make a parachute and suggest how to improve it.
- I will explain what I found out using my results and what I know about forces.
Get ready to explore the amazing world of forces and motion!
Key Words
- air resistance
- drag
- friction
- streamlined
- upthrust
- water resistance
Tap to Learn the Meanings!
- air resistance: A force that slows things down as they move through the air.
- drag: The force that resists the motion of an object moving through a fluid like air or water.
- friction: The force between two surfaces that slows them down when they slide over each other.
- streamlined: A smooth shape that helps objects move easily through air or water.
- upthrust: The upward force of water or air that helps objects float or rise.
- water resistance: A force that slows objects moving through water.
Excellent! You now know the forces that affect how things move through air and water.
🚴♂️ What is Friction?
In the picture, Marcus is riding his bike along a gravel path. The bike’s tyres and the gravel path try to slide past each other. The force between two surfaces that are trying to slide past each other is called friction. Friction only acts on moving objects. It always works in the direction opposite to the direction the object is moving, which slows it down.
🌊 Water and Air Resistance
Water resistance and air resistance are both types of friction. Water resistance slows down objects moving through water, while air resistance slows down objects moving through air. Air resistance affects all moving things on Earth. As an object moves, air pushes against it, reducing its speed.
💨 Drag Forces
Both water resistance and air resistance are sometimes called drag, because they drag back against the motion of the object and slow it down.
💧 Forces in Water
Have you ever tried to push a beach ball down into the sea or a swimming pool? The ball will not stay down because it floats on the surface. This happens because there is a force in the water that pushes things upward. This is called an upthrust force.
🐠 Streamlined Shapes and Drag
Any object that moves through water will be slowed down by the drag or water resistance. The shape of the object can help reduce this drag. Objects like fish have a sleek or streamlined shape, which causes less disturbance in the water and therefore less drag. Swimmers try to copy the streamlined shape of fish to move faster through the water.
Friction Opposes Motion 🚴♂️
Friction is the force between two surfaces that are trying to slide past each other. It only acts on moving objects and tries to stop the movement.
Friction’s Direction ↩️
Friction always acts in the direction opposite to the way an object is moving. This opposite push slows the object down.
Friction in Water and Air 💧🌬️
Water resistance is a kind of friction that slows things moving through water. Air resistance is a similar force that slows things moving through air.
Another Name: Drag 🏷️
Both water resistance and air resistance are often called drag, because they drag back against the movement.
Upthrust in Water 💦
There is an upward force in water that pushes things up. This force is called upthrust, and it helps floating objects stay on the surface.
Drag in Water and Streamlined Shapes 🐟
Any object moving through water is slowed down by water resistance (drag). A smooth, narrow, streamlined shape disturbs the water less and reduces drag.
Copying Nature 🏊
Swimmers try to copy the streamlined shape of fish to move more easily through the water.
What Is Air Resistance? 🌬️
Air resistance pushes against a moving object and slows it down. The larger the surface area of the object, the greater the air resistance.
Air Resistance on Falling Objects 🎈
Air resistance also acts on falling objects. Hot air balloons rise because heated gas inside the balloon is lighter than the air outside, and air resistance helps slow their fall.
Parachutes Use Air Resistance 🪂
Aparachute has a very large surface area that catches lots of air as it falls. This creates a lot of air resistance so a person can reach the ground slowly and safely.
Think like a Scientist – Compare Two Parachutes
You will need: thin string, a thin plastic sheet, sticky tape, two identical weights (such as small plastic toys), scissors, and a stopwatch.
How to make the parachutes:
- Cut two squares from the plastic sheet. One square must be 10 × 10 cm and the other 20 × 20 cm.
- Trim the edges with scissors to make each a neat eight-sided shape.
- Make a small hole with a pencil near the edge of each side.
- Thread a piece of string through each hole and tie knots so the string does not come out. All strings must be the same length.
- Join the ends of the eight strings with a knot.
- Attach the object you are using for a weight to the knot with sticky tape.
Think like a Scientist – Test Your Parachutes
Let's continue the parachute experiment!
Test your parachutes:
- Stand on a chair and raise your arm to drop your small parachute. Remember — drop it gently so it falls slowly!
- Use the stopwatch to time how many seconds it takes for the parachute to reach the ground.
- Repeat three times to check your results.
- Decide if you need to repeat more times to make your data more reliable.
- Record your results in a table.
- Predict whether the larger parachute will fall faster or slower than the small parachute.
- Repeat the steps with the large parachute to test your prediction.
Questions:
Tap to See Possible Answers
- 1: Gravity and air resistance acted on the parachute.
- 2: The diagram should show gravity pulling down and air resistance pushing up.
- 3 & 4: Calculate by adding all your times and dividing by three.
- 5: The larger parachute probably took longer to fall because it has a bigger surface area, creating more air resistance.
- 6: Make the parachute larger or use lighter material to increase air resistance.
- 7: Bigger parachutes fall more slowly because they catch more air, increasing air resistance and balancing gravity.
Excellent work — you tested variables just like a real scientist!
Think like a Scientist – How are we doing?
Answer the following questions about your group’s work on the parachute investigation.
For each question, choose one of these faces:
😊 😐 ☹️
- How well did we decide when measurements needed to be repeated to get more accurate data?
- How well did we measure time accurately and record our measurements?
- How well did we use our results and knowledge of forces to make a conclusion?
Tap to See Reflection Tips
- 😊 We worked carefully and repeated tests to make sure our data was reliable.
- 😐 We measured and recorded results but could improve our accuracy.
- ☹️ We need more practice to collect and use results correctly.
Great effort! Reflecting on how you worked helps you become a better scientist each time!