MUSIC PLAYING
Hi, everyone, I'm Mwaksy. I'm Greg.Quick question, Greg. Yes. So, I know if I let drop this apple,it will fall because of gravity. Yes.Ooh! Good catch.But what exactly is gravity?
Gravity is a force of attraction between any two objects.When you let go of the apple, it's pulled down towardsthe centre of the Earth. No matter what the object is,whether it's a falling apple or a jumping kangaroo,Earth's gravity will always pull everything downwards.Is the pull of gravity the same everywhere?
Well, it depends on the size of the objects causingthe gravity, so, their masses.For example, the force of gravity on themoon is smaller thanthe force of gravity on the Earthbecause the moon is made of less stuff.It has a much smaller mass.And actually, that lower force of gravity onthe moon means you can jump much higher there than on the Earth.OK, Greg, this sounds great,but I actually want to see this.So, show me the science!You've got it, because actually, I want to show you somethingpretty surprising.I've set up a simple experiment for us. Oooh.We have identical bottles, but mineI filled with more water than yours, OK?We're going to hold them from the same height,we're going to drop them at the same time. OK.And my question is,which bottle is going to hit the ground first, and why?Ooh. I'm thinkingthe red bottle will hit the ground first,because it has more water, and surelythat means it's heavier, right?Let's test it. OK. OK.Three, two, one…
BOTH: Drop! Oooh!
Wait, they fell at the same time.It's quite surprising, right? Yeah!You'd expect that the heavier bottle, the one that has more mass,is going to move much faster.But actually, it turns out that mass doesn't affecthow long it takes something to fall.Mind blown.
OK, question, Greg. Yes. If gravity pulls everything down,how does a helicopter stay up in the air?Ah, so, gravity is always pulling everything down,but you can overcome it with the right amount of force inthe opposite direction.A helicopter is very big and very heavy,which means there is a big force of gravity pulling it down.So, in order to lift it up off the ground,you need an even bigger upward force to overcome the gravity.A helicopter gets that upward force from its spinning blades.So, the higher you want something to go,the more upward force you would need to give it. Mm-hm.
So to launch a rocket into space,you would need a huge upward force to overcomethe downward force of Earth's gravity, is that right?Yes, spot-on. Yes!
Getting high enough to escape Earth's atmosphere takesa massive amount of force,which is why rockets have such enormous engines.Amazing. So gravity pulls everything downwards,all the time, but we can overcome gravity if we have enough force inthe opposite direction. Spot-on.Want to see this in action? I would love to. Allright.This is an air rocket.If you stomp your foot on there really hard,it pushes air up and round the tube,and that should give a nice upward force on the bottom of the rocketand launch it. Oh, wow.OK, shall we give it a go? Yeah.OK, please give me a countdown.Ready? OK.Three, two, one…Oh, come on. There it is!Yeah! You caught it!So, there was enough upward forceto overcome gravity and get it to launch. Uh-huh.Not enough upward force to get it into space. Ah!Next time. Yeah. And then gravity actually got the better of itand pulled it back down again. Right, that makes sense.OK, well, now we know what gravity is. Yeah. Yeah.So we're going to leave you with this one question.We've talked a lot about gravitytoday. Yeah.But there are, of course, other forces going on.So our question is, what are the other forces acting on the rocketbefore and during launch?Oh, that's a good one. I'm going to start thinking on that.Yeah, we'll see you next time. Bye! Bye!Go on, one more.Go on, do it!Whoa!Hasta la vista!
Video summary
Mwaksy and Greg look at how unsupported objects fall towards the Earth because of the force of gravity.
In a practical investigation, Mwaksy and Greg drop bottles with different amounts of liquid to find out which one will hit the ground first. The results are surprising!
After finding out about how much force is needed to lift a rocket, Mwaksy and Greg launch an air rocket.
Show Me the Science is a series of short films and teacher resources for primary schools, following presenters Mwaksy Mudenda and Greg Foot as they use demonstrations, experiments and animations to learn about forces and electricity.
Teacher Notes
Before watching the film:
Prior to this lesson you may wish to introduce students to other relevant topics, for example:
During the film:
Depending on your lesson’s focus, you may wish to pause the video at certain points to check for understanding, asking questions such as:
- Can you predict which bottle will fall to the ground first?
- Do you think gravity causes problems, or is it useful? What would happen if we didn’t have gravity?
- Rockets need a lot of upward force to get off the ground. Can you think of other examples where objects need to overcome gravity?
Final question:
What are the other forces acting on the rocket before and during launch?
Discussion points for the final question:
- You can watch this video of British astronaut Tim Peake’s journey to the International Space Station in 2015 to discuss what forces are acting upon the rocket: upward force (also called thrust), air resistance (also called drag), and gravity.
- You can return to this example after watching other videos in the Show Me the Science series.
Following on from the film:
- You can recreate the bottle drop experiment by using two bottles of the same size and different amounts of liquid. You can extend this further by dropping balls of playdough of different sizes.
- You can discuss how gravity can be useful by building a marble run. For this you will need craft materials, tape and marbles.
- You can link gravity to geography by discussing natural hazards such as landslides, rockfall or avalanches. These are examples of gravitational natural hazards as they occur because of gravity.
- Share this Bitesize article (that includes a quiz on gravity) with your students.
This short film is suitable for teaching science at KS2 in England, Wales and Northern Ireland and 2nd Level in Scotland.
What is friction? video
Mwaksy and Greg learn about friction, air resistance and water resistance, and see them in action.
What are levers? video
Mwaksy and Greg learn what levers are, what the different parts are called, and how they work.
What are magnets? video
Mwaksy and Greg learn about magnets, where they come from, and where magnetic materials can be found.
