Hold a medium apple on your open palm, then a full 1-liter water bottle, then a loaded backpack. Each one takes a bigger push from your hand to hold up. How much bigger? 'Bigger' will not do; forces get numbers.
A number needs a unit, and force has its own.
Holding up a medium apple takes a force of about 1 N. Holding up a full 1-liter water bottle takes about 10 N. Holding up a loaded backpack takes about 50 N.
The unit those three numbers share is the newton, written N: the SI unit of force. The newton is named after Isaac Newton, so its symbol is a capital N.
Which is the SI unit of force?
Keep the apple as your anchor: holding up one medium apple takes about 1 N.
Holding up which object takes a force of about 1 N?
Estimates scale from the anchors: holding three medium apples takes about 3 N, and holding two full 1-liter bottles takes about 20 N.
Jax carries a full 2-liter bottle of soda at his side. Which is the best estimate of the force his hand exerts to hold it up?
From here on, every force in this course comes with its number in newtons.
About how much force does holding up two medium apples take?
Holding up one medium apple takes about 1 N.
Two apples take about twice that.
About 2 N.
A digital force meter in a physics lab reads 15 N while Lena pulls on its hook. What does the 15 N measure?
The newton is the SI unit of force.
The meter's hook feels Lena's pull, and the display gives that pull's size.
The size of Lena's pull on the hook: a force of 15 N.
A digital force meter is hooked to a sled, and its display reads 12 N while Mira pulls. What does the reading measure?
Which is the best estimate of the force needed to hold up five medium apples?
Four readings are written on a lab whiteboard: 7.5 N, 7.5 kg, 7.5 m, 7.5 s. Which one could be the size of a force?