Week 1 - How do we measure forces and what is friction?
Welcome back to science. The topic this half term is Forces. Today we are going to be learning about how we measure forces and what friction is. You may remember some of the work as we will revise some of it from when you were in Year 3.
Task 1: Please watch the video below as revision from our forces work in year 3 when we learnt that types of forces can be pushes, pulls or twists.
There are many different types of forces. Some work in direct contact with objects, such as friction, air resistance and water resistance and are known as contact forces. Others work at a distance, such as magnetism and gravity and these forces are called non-contact forces. Friction is a force which opposes motion between moving surfaces in contact. The size of this force depends on the properties of the surfaces, (for example, the roughness.)
We can measure forces in units called Newtons using Newton metres. Here is a picture of some.
The hook on the end is attached to the object being pulled and the force of the pull is measured using the scale. The scales are different depending on the size of the force (or pull) on the object. It is important to choose the correct scale of Newton metre to match the size of the force you are measuring. The scales are indicated by the colours of the Newton metre. There are 2 scales on a Newton meter, grams and Newtons. Grams is the measurement of mass but we will be using Newtons which is the unit of force.
Task 2: Please complete the sheet below to practise reading the scales on these Newton meters.
Today we are going to be learning about a force called friction. You may remember learning about it during our forces topic in year 3. It is a contact force which acts between two surfaces. It slows moving objects down. Please watch the videos below to learn more about it.
As you have heard, smooth surfaces create less friction and rough surfaces create more. Sometimes it is important for us to reduce friction. For example in a machine where two bits of metal move against each other or when skiing on snow or iceskating. We can add a lubricant to the surface of the object to reduce friction. You can feel the effect of reducing the friction between your hands when you do task 2 below.
Task 2: Make sure that your hands are dry. Rub your hands together vigorously. What happens to their temperature? Now add some hand lotion and rub them again. What happens this time? What was the lubricant in this activity?
At other times it is important to increase friction. For example to prevent objects slipping on icy surfaces. Our shoes have treads on the bottom of them to increase their grip by increasing the friction between the bottom of the shoe and the surface we walk on. It is the same with car tyres too.
Task 3: Please read through this experiment and answer the questions, then send your work to me in Teams.
Extension activity: You could make one of the cardboard hover discs which were shown in the Science Max video, or test which surface has the least/most friction by measuring how far an object will travel down a ramp with different surfaces or along different surfaces when pushed with the same amount of force.
Optional video: Find out what reduces the friction as glaciers move across the ground by watching the video below.